Quotient rule
Objective. Differentiate quotients while preserving structure.
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- 2. Worked example
- 3. Practice
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Learn: the key idea
The quotient rule differentiates one function divided by another. If y = u/v, then dy/dx = (v(du/dx) − u(dv/dx))/v². The order in the numerator matters: the denominator's derivative term is subtracted, not added, and the whole expression is divided by v squared. For example, if y = x²/(x+1), with u = x² and v = x+1, dy/dx = ((x+1)(2x) − x²(1))/(x+1)². Always keep u and v in a fixed order and subtract carefully.
Worked example
Differentiate y = (2x)/(x² + 1) using the quotient rule.
- 1Let u = 2x and v = x² + 1, so du/dx = 2 and dv/dx = 2x
- 2Apply dy/dx = (v(du/dx) − u(dv/dx))/v²
- 3dy/dx = ((x²+1)(2) − 2x(2x))/(x²+1)²
- 4Expand and simplify to dy/dx = (2 − 2x²)/(x²+1)²
Answer: dy/dx = (2 − 2x²)/(x²+1)²
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Practice
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Start practisingCommon mistake. Students often reverse the subtraction order, writing u(dv/dx) − v(du/dx) instead of v(du/dx) − u(dv/dx), which flips the sign. Fix this by always writing the denominator's derivative term first.
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