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Chain Rule, Log Differentiation & Rate of Change · Question 88 of 130

Question 88

MediumOriginal question

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

Options for question 88

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

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

  2. At 0: y=6y = 6 and y′y=1+12+13=116\frac{y'}{y} = 1 + \frac{1}{2} + \frac{1}{3} = \frac{11}{6}, so y′=11y' = 11.

Worth noting

116\frac{11}{6} is y′y\frac{y'}{y}; multiply by y(0)=6y(0) = 6.

Concept
Logarithmic differentiation of a product
Typical time
90 s
Your time
—
The rule this testsLogarithmic differentiation
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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.