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Chain Rule, Log Differentiation & Rate of Change · Question 96 of 130

Question 96

HardOriginal question

If f(x)=(x+1)2(x+2)3f(x) = \left(x + 1\right)^{2} \left(x + 2\right)^{3}, what is f′(0)f'\left(0\right)?

Options for question 96

Show the answer and explanation
CorrectNot quiteAnswer C

Correct answer: C

Explanation

  1. log⁡y=2log⁡(x+1)+3log⁡(x+2)\log y = 2\log(x + 1) + 3\log(x + 2), so y′y=2x+1+3x+2\frac{y'}{y} = \frac{2}{x + 1} + \frac{3}{x + 2}.

  2. At 0: y=8y = 8 and y′y=2+32=72\frac{y'}{y} = 2 + \frac{3}{2} = \frac{7}{2}, so y′=28y' = 28.

Worth noting

72\frac{7}{2} is y′y\frac{y'}{y}; multiply by y(0)=8y(0) = 8 to get y′y'.

Concept
Logarithmic differentiation of a product
Typical time
120 s
Your time
—
The rule this testsLogarithmic differentiation
Practise this chapter →

Ten questions from Chain Rule, Log Differentiation & Rate of Change, at your own pace.

Practise this chapter →

Ten questions from Chain Rule, Log Differentiation & Rate of Change, at your own pace.