diff --git a/content/lessons/quant/quant-arithmetic-exponents-roots.md b/content/lessons/quant/quant-arithmetic-exponents-roots.md new file mode 100644 index 0000000..1770d0e --- /dev/null +++ b/content/lessons/quant/quant-arithmetic-exponents-roots.md @@ -0,0 +1,75 @@ +--- +id: quant-arithmetic-exponents-roots +section: quant +topic: arithmetic +subtopic: exponents-roots +title: "Exponents & Roots" +tags: [exponents, roots, powers, radicals] +author: openmat +reviewers: [] +status: in-review +original: true +license: CC-BY-SA-4.0 +--- + +## Overview + +Exponents and roots show up all over GMAT Focus Quant — in number properties, algebra, and word +problems (growth, interest, doubling). Almost every question is solved by applying a small set of +**exponent rules** rather than by grinding out large powers. Learn the rules cold and most of +these problems become one or two lines. + +## Core concepts + +**The exponent rules.** For any nonzero base and integer exponents: + +\[a^m \cdot a^n = a^{m+n}, \qquad \frac{a^m}{a^n} = a^{m-n}, \qquad (a^m)^n = a^{mn}\] + +\[(ab)^n = a^n b^n, \qquad \left(\frac{a}{b}\right)^n = \frac{a^n}{b^n}\] + +**Zero and negative exponents.** + +\[a^0 = 1 \ (a \neq 0), \qquad a^{-n} = \frac{1}{a^n}\] + +A negative exponent means "reciprocal," not "negative number": \(2^{-3} = \tfrac{1}{8}\), not \(-8\). + +**Common-base is the master move.** To compare or solve, rewrite everything as a power of the same +base. If \(a^x = a^y\) (and \(a \neq 0, \pm 1\)), then \(x = y\). Example: \(4^3 = (2^2)^3 = 2^6\), +so \(4^3\) and \(8^2 = (2^3)^2 = 2^6\) are equal. + +**Roots are fractional exponents.** + +\[\sqrt{a} = a^{1/2}, \qquad \sqrt[n]{a} = a^{1/n}, \qquad \sqrt[n]{a^m} = a^{m/n}\] + +So the exponent rules apply to roots too. Simplify radicals by pulling out perfect-square factors: +\(\sqrt{72} = \sqrt{36 \cdot 2} = 6\sqrt{2}\). + +**Multiply and divide radicals** freely: \(\sqrt{a}\,\sqrt{b} = \sqrt{ab}\) and +\(\dfrac{\sqrt{a}}{\sqrt{b}} = \sqrt{\tfrac{a}{b}}\). But **you cannot add** across a root: +\(\sqrt{a+b} \neq \sqrt{a} + \sqrt{b}\). + +## Worked examples + +**Common base.** Solve \(2^{x} = 32\). Since \(32 = 2^5\), \(x = 5\). + +**Combine, don't compute.** \(\dfrac{3^{10}}{3^{7}} = 3^{10-7} = 3^3 = 27\) — never expand \(3^{10}\). + +**Factor out the common power.** \(2^{11} + 2^{11} = 2 \cdot 2^{11} = 2^{12}\). Adding equal powers +*doubles*; it does not add the exponents. + +**Simplify a radical.** \(\sqrt{50} + \sqrt{18} = 5\sqrt{2} + 3\sqrt{2} = 8\sqrt{2}\). + +## Common traps + +- **Adding exponents when multiplying bases.** \(2^3 \cdot 3^3 \neq 6^6\). Same *exponent*, different + base: \(2^3 \cdot 3^3 = (2\cdot 3)^3 = 6^3\). Add exponents only for the *same base*. +- **Adding across a root or a sum of powers.** \(\sqrt{9+16} = \sqrt{25} = 5\), not \(3+4=7\). +- **Mishandling negative exponents.** \(a^{-n}\) is a reciprocal, not a negative value. +- **Forgetting \(a^0 = 1\).** Any nonzero base to the zero power is 1, regardless of the base. + +## Key takeaways + +- Multiply → add exponents; divide → subtract; power of a power → multiply. Same base only. +- Rewrite everything to a **common base** to compare or solve equations with exponents. +- Roots are fractional exponents; simplify by extracting perfect-square factors. +- You can multiply and divide radicals, but you cannot split a root over addition. diff --git a/content/questions/quant/quant-arithmetic-exponents-roots-0017.md b/content/questions/quant/quant-arithmetic-exponents-roots-0017.md new file mode 100644 index 0000000..671bc55 --- /dev/null +++ b/content/questions/quant/quant-arithmetic-exponents-roots-0017.md @@ -0,0 +1,42 @@ +--- +id: quant-arithmetic-exponents-roots-0017 +section: quant +topic: arithmetic +subtopic: exponents-roots +type: problem-solving +difficulty: easy +tags: [exponents, common-base] +choices: + A: "3" + B: "4" + C: "5" + D: "6" + E: "8" +answer: C +author: openmat +reviewers: [] +status: in-review +original: true +license: CC-BY-SA-4.0 +--- + +## Question + +If \(2^{x} = 32\), what is the value of \(x\)? + +## Explanation + +Rewrite the right side as a power of the same base, 2. Since \(32 = 2 \times 2 \times 2 \times 2 +\times 2 = 2^5\), the equation becomes: + +\[2^{x} = 2^{5}\] + +When two equal powers share the same base, their exponents must be equal, so \(x = 5\). + +**The trap:** answer **E (8)** comes from computing \(32 \div 4\) or otherwise treating the problem +as arithmetic rather than matching exponents. Don't multiply — match the base. + +## Hints + +- Write 32 as a power of 2. +- If \(2^x = 2^5\), what must \(x\) be? diff --git a/content/questions/quant/quant-arithmetic-exponents-roots-0018.md b/content/questions/quant/quant-arithmetic-exponents-roots-0018.md new file mode 100644 index 0000000..62b910b --- /dev/null +++ b/content/questions/quant/quant-arithmetic-exponents-roots-0018.md @@ -0,0 +1,42 @@ +--- +id: quant-arithmetic-exponents-roots-0018 +section: quant +topic: arithmetic +subtopic: exponents-roots +type: problem-solving +difficulty: easy +tags: [exponents, division, common-base] +choices: + A: "9" + B: "27" + C: "81" + D: "243" + E: "729" +answer: B +author: openmat +reviewers: [] +status: in-review +original: true +license: CC-BY-SA-4.0 +--- + +## Question + +What is the value of \(\dfrac{3^{10}}{3^{7}}\)? + +## Explanation + +Never expand \(3^{10}\). When you divide powers of the same base, **subtract** the exponents: + +\[\frac{3^{10}}{3^{7}} = 3^{10 - 7} = 3^{3}\] + +And \(3^3 = 27\). + +**The trap:** answer **E (729)** is \(3^6\), which you'd get by mistakenly *dividing* the exponents +(\(10 \div 7\) rounded, or similar) or by other slips. Division of like bases means subtracting +exponents, not dividing them. + +## Hints + +- Same base, division → subtract the exponents. +- Compute \(3^{10-7}\). diff --git a/content/questions/quant/quant-arithmetic-exponents-roots-0019.md b/content/questions/quant/quant-arithmetic-exponents-roots-0019.md new file mode 100644 index 0000000..6072d1a --- /dev/null +++ b/content/questions/quant/quant-arithmetic-exponents-roots-0019.md @@ -0,0 +1,42 @@ +--- +id: quant-arithmetic-exponents-roots-0019 +section: quant +topic: arithmetic +subtopic: exponents-roots +type: problem-solving +difficulty: medium +tags: [exponents, negative-exponents, fractions] +choices: + A: "-8" + B: "-\\tfrac{1}{8}" + C: "\\tfrac{1}{8}" + D: "\\tfrac{1}{6}" + E: "8" +answer: C +author: openmat +reviewers: [] +status: in-review +original: true +license: CC-BY-SA-4.0 +--- + +## Question + +What is the value of \(2^{-3}\)? + +## Explanation + +A negative exponent means "take the reciprocal," not "make the result negative." By the rule +\(a^{-n} = \dfrac{1}{a^{n}}\): + +\[2^{-3} = \frac{1}{2^{3}} = \frac{1}{8}\] + +**The trap:** answer **A (\(-8\))** treats the negative sign as if it made the value negative, and +**B** repeats that error inside the fraction. The exponent's sign controls reciprocal-vs-not, not +the sign of the answer. Choice **D (\(\tfrac{1}{6}\))** comes from computing \(2 \times 3\) in the +denominator instead of \(2^3\). + +## Hints + +- \(a^{-n}\) is the reciprocal of \(a^{n}\), and stays positive. +- The denominator is \(2^3\), not \(2 \times 3\). diff --git a/content/questions/quant/quant-arithmetic-exponents-roots-0020.md b/content/questions/quant/quant-arithmetic-exponents-roots-0020.md new file mode 100644 index 0000000..72821ff --- /dev/null +++ b/content/questions/quant/quant-arithmetic-exponents-roots-0020.md @@ -0,0 +1,44 @@ +--- +id: quant-arithmetic-exponents-roots-0020 +section: quant +topic: arithmetic +subtopic: exponents-roots +type: problem-solving +difficulty: medium +tags: [exponents, adding-powers, factoring] +choices: + A: "2^{11}" + B: "2^{12}" + C: "2^{22}" + D: "4^{11}" + E: "4^{22}" +answer: B +author: openmat +reviewers: [] +status: in-review +original: true +license: CC-BY-SA-4.0 +--- + +## Question + +Which of the following is equal to \(2^{11} + 2^{11}\)? + +## Explanation + +You are **adding** two equal quantities, so the result is twice one of them: + +\[2^{11} + 2^{11} = 2 \times 2^{11}\] + +Now \(2 = 2^1\), and multiplying like bases means adding exponents: + +\[2^{1} \times 2^{11} = 2^{1+11} = 2^{12}\] + +**The trap:** answer **C (\(2^{22}\))** comes from adding the exponents (\(11 + 11\)) as if the two +terms were multiplied. They are added, so the powers double — increasing the exponent by exactly 1. +Choice **D (\(4^{11}\))** looks tempting but \(4^{11} = 2^{22}\), the same wrong value. + +## Hints + +- Adding two equal terms means multiplying one of them by 2. +- Write the leading 2 as \(2^1\), then combine like bases. diff --git a/content/questions/quant/quant-arithmetic-exponents-roots-0021.md b/content/questions/quant/quant-arithmetic-exponents-roots-0021.md new file mode 100644 index 0000000..c329752 --- /dev/null +++ b/content/questions/quant/quant-arithmetic-exponents-roots-0021.md @@ -0,0 +1,45 @@ +--- +id: quant-arithmetic-exponents-roots-0021 +section: quant +topic: arithmetic +subtopic: exponents-roots +type: problem-solving +difficulty: medium +tags: [roots, radicals, simplifying] +choices: + A: "5\\sqrt{2}" + B: "8\\sqrt{2}" + C: "\\sqrt{68}" + D: "34" + E: "68" +answer: B +author: openmat +reviewers: [] +status: in-review +original: true +license: CC-BY-SA-4.0 +--- + +## Question + +What is \(\sqrt{50} + \sqrt{18}\) in simplest form? + +## Explanation + +Simplify each radical by pulling out its largest perfect-square factor, then combine like terms. + +\[\sqrt{50} = \sqrt{25 \cdot 2} = 5\sqrt{2}\] +\[\sqrt{18} = \sqrt{9 \cdot 2} = 3\sqrt{2}\] + +Both are multiples of \(\sqrt{2}\), so add the coefficients: + +\[5\sqrt{2} + 3\sqrt{2} = 8\sqrt{2}\] + +**The trap:** answer **C (\(\sqrt{68}\))** comes from adding *under* the radical +(\(\sqrt{50+18}\)) — you cannot split or combine a root over addition that way. You must simplify +each radical first, then add the like radical terms. + +## Hints + +- \(\sqrt{a+b} \neq \sqrt{a} + \sqrt{b}\) — don't add inside the root. +- Extract perfect-square factors from 50 and 18, then combine the \(\sqrt{2}\) terms. diff --git a/content/questions/quant/quant-arithmetic-exponents-roots-0022.md b/content/questions/quant/quant-arithmetic-exponents-roots-0022.md new file mode 100644 index 0000000..83bda05 --- /dev/null +++ b/content/questions/quant/quant-arithmetic-exponents-roots-0022.md @@ -0,0 +1,53 @@ +--- +id: quant-arithmetic-exponents-roots-0022 +section: quant +topic: arithmetic +subtopic: exponents-roots +type: problem-solving +difficulty: hard +tags: [exponents, common-base, power-of-a-power] +choices: + A: "2" + B: "3" + C: "4" + D: "5" + E: "6" +answer: A +author: openmat +reviewers: [] +status: in-review +original: true +license: CC-BY-SA-4.0 +--- + +## Question + +If \(9^{x} \cdot 27 = 3^{7}\), what is the value of \(x\)? + +## Explanation + +Rewrite every term as a power of the common base 3. + +- \(9 = 3^2\), so \(9^{x} = (3^2)^{x} = 3^{2x}\) (power of a power → multiply exponents). +- \(27 = 3^3\). + +Substitute: + +\[3^{2x} \cdot 3^{3} = 3^{7}\] + +Multiplying like bases adds exponents on the left: + +\[3^{2x + 3} = 3^{7}\] + +Now the bases match, so set the exponents equal: + +\[2x + 3 = 7 \;\Rightarrow\; 2x = 4 \;\Rightarrow\; x = 2\] + +**The trap:** answer **C (4)** is the value of \(2x\) — easy to stop one step early. Answer **D (5)** +comes from forgetting to rewrite 27 and using \(2x + 2 = 7\) or a similar slip. Convert *every* term +to base 3 before equating exponents. + +## Hints + +- Rewrite 9 and 27 as powers of 3. +- \((3^2)^x = 3^{2x}\); then add exponents on the left and set them equal to 7. diff --git a/curriculum.md b/curriculum.md index 5ad658a..9c583e2 100644 --- a/curriculum.md +++ b/curriculum.md @@ -70,7 +70,7 @@ The taxonomy is ordered so you can study a section top to bottom. A balanced pla Early days — the bank is growing. Rough coverage so far (a contributor could automate this count from the front-matter): -- **Quant** — arithmetic, number properties, algebra (linear, inequalities), word problems (rates, work, sets), counting & probability, statistics (mean, median, weighted average, standard deviation). +- **Quant** — arithmetic (fractions, percents/ratios, exponents & roots), number properties, algebra (linear, quadratics, inequalities), word problems (rates, work, sets), counting & probability, statistics (mean, median, weighted average, standard deviation). - **Verbal** — Critical Reasoning (assumptions, strengthen/weaken, inference, flaw) and Reading Comprehension (main idea, detail/inference). - **Data Insights** — Data Sufficiency across fundamentals, divisibility, number properties, algebra, statistics, word problems, and overlapping sets. diff --git a/docs/data/content.json b/docs/data/content.json index 9ef981c..58c647d 100644 --- a/docs/data/content.json +++ b/docs/data/content.json @@ -7,8 +7,8 @@ "stats": { "quant": { "label": "Quantitative", - "questions": 16, - "lessons": 5 + "questions": 22, + "lessons": 6 }, "verbal": { "label": "Verbal", @@ -22,8 +22,8 @@ } }, "counts": { - "questions": 32, - "lessons": 8 + "questions": 38, + "lessons": 9 }, "questions": [ { @@ -301,6 +301,185 @@ "Or use the coefficient shortcut: sum of roots \\(= -b\\), product \\(= c\\)." ] }, + { + "id": "quant-arithmetic-exponents-roots-0017", + "section": "quant", + "topic": "arithmetic", + "subtopic": "exponents-roots", + "type": "problem-solving", + "difficulty": "easy", + "tags": [ + "exponents", + "common-base" + ], + "choices": { + "A": "3", + "B": "4", + "C": "5", + "D": "6", + "E": "8" + }, + "answer": "C", + "author": "openmat", + "reviewers": [], + "status": "in-review", + "prompt": "If \\(2^{x} = 32\\), what is the value of \\(x\\)?", + "explanation": "Rewrite the right side as a power of the same base, 2. Since \\(32 = 2 \\times 2 \\times 2 \\times 2\n\\times 2 = 2^5\\), the equation becomes:\n\n\\[2^{x} = 2^{5}\\]\n\nWhen two equal powers share the same base, their exponents must be equal, so \\(x = 5\\).\n\n**The trap:** answer **E (8)** comes from computing \\(32 \\div 4\\) or otherwise treating the problem\nas arithmetic rather than matching exponents. Don't multiply — match the base.", + "hints": [ + "Write 32 as a power of 2.", + "If \\(2^x = 2^5\\), what must \\(x\\) be?" + ] + }, + { + "id": "quant-arithmetic-exponents-roots-0018", + "section": "quant", + "topic": "arithmetic", + "subtopic": "exponents-roots", + "type": "problem-solving", + "difficulty": "easy", + "tags": [ + "exponents", + "division", + "common-base" + ], + "choices": { + "A": "9", + "B": "27", + "C": "81", + "D": "243", + "E": "729" + }, + "answer": "B", + "author": "openmat", + "reviewers": [], + "status": "in-review", + "prompt": "What is the value of \\(\\dfrac{3^{10}}{3^{7}}\\)?", + "explanation": "Never expand \\(3^{10}\\). When you divide powers of the same base, **subtract** the exponents:\n\n\\[\\frac{3^{10}}{3^{7}} = 3^{10 - 7} = 3^{3}\\]\n\nAnd \\(3^3 = 27\\).\n\n**The trap:** answer **E (729)** is \\(3^6\\), which you'd get by mistakenly *dividing* the exponents\n(\\(10 \\div 7\\) rounded, or similar) or by other slips. Division of like bases means subtracting\nexponents, not dividing them.", + "hints": [ + "Same base, division → subtract the exponents.", + "Compute \\(3^{10-7}\\)." + ] + }, + { + "id": "quant-arithmetic-exponents-roots-0019", + "section": "quant", + "topic": "arithmetic", + "subtopic": "exponents-roots", + "type": "problem-solving", + "difficulty": "medium", + "tags": [ + "exponents", + "negative-exponents", + "fractions" + ], + "choices": { + "A": "-8", + "B": "-\\\\tfrac{1}{8}", + "C": "\\\\tfrac{1}{8}", + "D": "\\\\tfrac{1}{6}", + "E": "8" + }, + "answer": "C", + "author": "openmat", + "reviewers": [], + "status": "in-review", + "prompt": "What is the value of \\(2^{-3}\\)?", + "explanation": "A negative exponent means \"take the reciprocal,\" not \"make the result negative.\" By the rule\n\\(a^{-n} = \\dfrac{1}{a^{n}}\\):\n\n\\[2^{-3} = \\frac{1}{2^{3}} = \\frac{1}{8}\\]\n\n**The trap:** answer **A (\\(-8\\))** treats the negative sign as if it made the value negative, and\n**B** repeats that error inside the fraction. The exponent's sign controls reciprocal-vs-not, not\nthe sign of the answer. Choice **D (\\(\\tfrac{1}{6}\\))** comes from computing \\(2 \\times 3\\) in the\ndenominator instead of \\(2^3\\).", + "hints": [ + "\\(a^{-n}\\) is the reciprocal of \\(a^{n}\\), and stays positive.", + "The denominator is \\(2^3\\), not \\(2 \\times 3\\)." + ] + }, + { + "id": "quant-arithmetic-exponents-roots-0020", + "section": "quant", + "topic": "arithmetic", + "subtopic": "exponents-roots", + "type": "problem-solving", + "difficulty": "medium", + "tags": [ + "exponents", + "adding-powers", + "factoring" + ], + "choices": { + "A": "2^{11}", + "B": "2^{12}", + "C": "2^{22}", + "D": "4^{11}", + "E": "4^{22}" + }, + "answer": "B", + "author": "openmat", + "reviewers": [], + "status": "in-review", + "prompt": "Which of the following is equal to \\(2^{11} + 2^{11}\\)?", + "explanation": "You are **adding** two equal quantities, so the result is twice one of them:\n\n\\[2^{11} + 2^{11} = 2 \\times 2^{11}\\]\n\nNow \\(2 = 2^1\\), and multiplying like bases means adding exponents:\n\n\\[2^{1} \\times 2^{11} = 2^{1+11} = 2^{12}\\]\n\n**The trap:** answer **C (\\(2^{22}\\))** comes from adding the exponents (\\(11 + 11\\)) as if the two\nterms were multiplied. They are added, so the powers double — increasing the exponent by exactly 1.\nChoice **D (\\(4^{11}\\))** looks tempting but \\(4^{11} = 2^{22}\\), the same wrong value.", + "hints": [ + "Adding two equal terms means multiplying one of them by 2.", + "Write the leading 2 as \\(2^1\\), then combine like bases." + ] + }, + { + "id": "quant-arithmetic-exponents-roots-0021", + "section": "quant", + "topic": "arithmetic", + "subtopic": "exponents-roots", + "type": "problem-solving", + "difficulty": "medium", + "tags": [ + "roots", + "radicals", + "simplifying" + ], + "choices": { + "A": "5\\\\sqrt{2}", + "B": "8\\\\sqrt{2}", + "C": "\\\\sqrt{68}", + "D": "34", + "E": "68" + }, + "answer": "B", + "author": "openmat", + "reviewers": [], + "status": "in-review", + "prompt": "What is \\(\\sqrt{50} + \\sqrt{18}\\) in simplest form?", + "explanation": "Simplify each radical by pulling out its largest perfect-square factor, then combine like terms.\n\n\\[\\sqrt{50} = \\sqrt{25 \\cdot 2} = 5\\sqrt{2}\\]\n\\[\\sqrt{18} = \\sqrt{9 \\cdot 2} = 3\\sqrt{2}\\]\n\nBoth are multiples of \\(\\sqrt{2}\\), so add the coefficients:\n\n\\[5\\sqrt{2} + 3\\sqrt{2} = 8\\sqrt{2}\\]\n\n**The trap:** answer **C (\\(\\sqrt{68}\\))** comes from adding *under* the radical\n(\\(\\sqrt{50+18}\\)) — you cannot split or combine a root over addition that way. You must simplify\neach radical first, then add the like radical terms.", + "hints": [ + "\\(\\sqrt{a+b} \\neq \\sqrt{a} + \\sqrt{b}\\) — don't add inside the root.", + "Extract perfect-square factors from 50 and 18, then combine the \\(\\sqrt{2}\\) terms." + ] + }, + { + "id": "quant-arithmetic-exponents-roots-0022", + "section": "quant", + "topic": "arithmetic", + "subtopic": "exponents-roots", + "type": "problem-solving", + "difficulty": "hard", + "tags": [ + "exponents", + "common-base", + "power-of-a-power" + ], + "choices": { + "A": "2", + "B": "3", + "C": "4", + "D": "5", + "E": "6" + }, + "answer": "A", + "author": "openmat", + "reviewers": [], + "status": "in-review", + "prompt": "If \\(9^{x} \\cdot 27 = 3^{7}\\), what is the value of \\(x\\)?", + "explanation": "Rewrite every term as a power of the common base 3.\n\n- \\(9 = 3^2\\), so \\(9^{x} = (3^2)^{x} = 3^{2x}\\) (power of a power → multiply exponents).\n- \\(27 = 3^3\\).\n\nSubstitute:\n\n\\[3^{2x} \\cdot 3^{3} = 3^{7}\\]\n\nMultiplying like bases adds exponents on the left:\n\n\\[3^{2x + 3} = 3^{7}\\]\n\nNow the bases match, so set the exponents equal:\n\n\\[2x + 3 = 7 \\;\\Rightarrow\\; 2x = 4 \\;\\Rightarrow\\; x = 2\\]\n\n**The trap:** answer **C (4)** is the value of \\(2x\\) — easy to stop one step early. Answer **D (5)**\ncomes from forgetting to rewrite 27 and using \\(2x + 2 = 7\\) or a similar slip. Convert *every* term\nto base 3 before equating exponents.", + "hints": [ + "Rewrite 9 and 27 as powers of 3.", + "\\((3^2)^x = 3^{2x}\\); then add exponents on the left and set them equal to 7." + ] + }, { "id": "quant-arithmetic-fractions-decimals-0015", "section": "quant", @@ -968,6 +1147,23 @@ "status": "in-review", "body": "## Overview\n\nA quadratic equation has the form \\(ax^2 + bx + c = 0\\). On GMAT Focus Quant, most quadratics are\nbuilt to **factor cleanly**, so factoring — not the quadratic formula — is usually the fast route.\n\n## Core concepts\n\n**Factoring \\(x^2 + bx + c\\).** Find two numbers that **multiply to \\(c\\)** and **add to \\(b\\)**.\nThen \\(x^2 + bx + c = (x + p)(x + q)\\), and the solutions make each factor zero.\n\nExample: \\(x^2 - 5x + 6\\). Two numbers multiplying to \\(+6\\) and adding to \\(-5\\) are \\(-2\\) and\n\\(-3\\), so \\((x-2)(x-3) = 0\\) and \\(x = 2\\) or \\(x = 3\\).\n\n**Sum and product shortcut.** For \\(x^2 + bx + c = 0\\):\n\n\\[\\text{sum of roots} = -b, \\qquad \\text{product of roots} = c\\]\n\nThis lets you answer \"sum/product of solutions\" questions without fully solving.\n\n**Special products** worth recognizing instantly:\n\n\\[a^2 - b^2 = (a-b)(a+b), \\quad (a+b)^2 = a^2 + 2ab + b^2, \\quad (a-b)^2 = a^2 - 2ab + b^2\\]\n\n**The quadratic formula** (fallback when factoring is ugly):\n\n\\[x = \\frac{-b \\pm \\sqrt{b^2 - 4ac}}{2a}\\]\n\n## Worked examples\n\n**Factor and solve.** \\(x^2 + 2x - 15 = 0 \\Rightarrow (x+5)(x-3) = 0 \\Rightarrow x = -5 \\text{ or } 3\\).\n\n**Difference of squares.** \\(x^2 - 49 = 0 \\Rightarrow (x-7)(x+7) = 0 \\Rightarrow x = \\pm 7\\).\n\n## Common traps\n\n- **Confusing sum and product of roots.** Sum is \\(-b\\), product is \\(c\\). Read which the question wants.\n- **Dropping a solution.** A quadratic usually has *two* roots — check whether the question wants both, their sum, or only positive values.\n- **Sign errors in factoring.** Verify by expanding your factors back out.\n\n## Key takeaways\n\n- Factor into \\((x + p)(x + q)\\) where \\(pq = c\\) and \\(p + q = b\\); each factor set to zero gives a root.\n- Sum of roots \\(= -b\\), product \\(= c\\) — a fast shortcut.\n- Recognize the difference of squares and perfect-square forms on sight." }, + { + "id": "quant-arithmetic-exponents-roots", + "section": "quant", + "topic": "arithmetic", + "subtopic": "exponents-roots", + "title": "Exponents & Roots", + "tags": [ + "exponents", + "roots", + "powers", + "radicals" + ], + "author": "openmat", + "reviewers": [], + "status": "in-review", + "body": "## Overview\n\nExponents and roots show up all over GMAT Focus Quant — in number properties, algebra, and word\nproblems (growth, interest, doubling). Almost every question is solved by applying a small set of\n**exponent rules** rather than by grinding out large powers. Learn the rules cold and most of\nthese problems become one or two lines.\n\n## Core concepts\n\n**The exponent rules.** For any nonzero base and integer exponents:\n\n\\[a^m \\cdot a^n = a^{m+n}, \\qquad \\frac{a^m}{a^n} = a^{m-n}, \\qquad (a^m)^n = a^{mn}\\]\n\n\\[(ab)^n = a^n b^n, \\qquad \\left(\\frac{a}{b}\\right)^n = \\frac{a^n}{b^n}\\]\n\n**Zero and negative exponents.**\n\n\\[a^0 = 1 \\ (a \\neq 0), \\qquad a^{-n} = \\frac{1}{a^n}\\]\n\nA negative exponent means \"reciprocal,\" not \"negative number\": \\(2^{-3} = \\tfrac{1}{8}\\), not \\(-8\\).\n\n**Common-base is the master move.** To compare or solve, rewrite everything as a power of the same\nbase. If \\(a^x = a^y\\) (and \\(a \\neq 0, \\pm 1\\)), then \\(x = y\\). Example: \\(4^3 = (2^2)^3 = 2^6\\),\nso \\(4^3\\) and \\(8^2 = (2^3)^2 = 2^6\\) are equal.\n\n**Roots are fractional exponents.**\n\n\\[\\sqrt{a} = a^{1/2}, \\qquad \\sqrt[n]{a} = a^{1/n}, \\qquad \\sqrt[n]{a^m} = a^{m/n}\\]\n\nSo the exponent rules apply to roots too. Simplify radicals by pulling out perfect-square factors:\n\\(\\sqrt{72} = \\sqrt{36 \\cdot 2} = 6\\sqrt{2}\\).\n\n**Multiply and divide radicals** freely: \\(\\sqrt{a}\\,\\sqrt{b} = \\sqrt{ab}\\) and\n\\(\\dfrac{\\sqrt{a}}{\\sqrt{b}} = \\sqrt{\\tfrac{a}{b}}\\). But **you cannot add** across a root:\n\\(\\sqrt{a+b} \\neq \\sqrt{a} + \\sqrt{b}\\).\n\n## Worked examples\n\n**Common base.** Solve \\(2^{x} = 32\\). Since \\(32 = 2^5\\), \\(x = 5\\).\n\n**Combine, don't compute.** \\(\\dfrac{3^{10}}{3^{7}} = 3^{10-7} = 3^3 = 27\\) — never expand \\(3^{10}\\).\n\n**Factor out the common power.** \\(2^{11} + 2^{11} = 2 \\cdot 2^{11} = 2^{12}\\). Adding equal powers\n*doubles*; it does not add the exponents.\n\n**Simplify a radical.** \\(\\sqrt{50} + \\sqrt{18} = 5\\sqrt{2} + 3\\sqrt{2} = 8\\sqrt{2}\\).\n\n## Common traps\n\n- **Adding exponents when multiplying bases.** \\(2^3 \\cdot 3^3 \\neq 6^6\\). Same *exponent*, different\n base: \\(2^3 \\cdot 3^3 = (2\\cdot 3)^3 = 6^3\\). Add exponents only for the *same base*.\n- **Adding across a root or a sum of powers.** \\(\\sqrt{9+16} = \\sqrt{25} = 5\\), not \\(3+4=7\\).\n- **Mishandling negative exponents.** \\(a^{-n}\\) is a reciprocal, not a negative value.\n- **Forgetting \\(a^0 = 1\\).** Any nonzero base to the zero power is 1, regardless of the base.\n\n## Key takeaways\n\n- Multiply → add exponents; divide → subtract; power of a power → multiply. Same base only.\n- Rewrite everything to a **common base** to compare or solve equations with exponents.\n- Roots are fractional exponents; simplify by extracting perfect-square factors.\n- You can multiply and divide radicals, but you cannot split a root over addition." + }, { "id": "quant-arithmetic-percents-ratios", "section": "quant",