Keep calm and Apply Chain Rule

Calculus Level 2

f ( x ) = exp ( 2 sin ( x ( 3 log 5 ) ) ) f(x)=\exp(2 \sin(x^{(3 \log 5)}))

Evaluate f ( 5 ) f'(5) to 2 decimal places.

Clarification:

  • log \log is the natural logarithm (base e e )

  • exp ( x ) \exp(x) is the exponential function , e x e^{x}


The answer is -6572.05.

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1 solution

Spencer Whitehead
Feb 29, 2016

The easiest way to do this is simply to solve for the derivative of f f , then evaluate it at x = 5 x=5 . We note that the function can be written as a composition of functions, and thus is solvable using chain rule:

d d x f ( x ) = e ( 2 sin ( x ( 3 log 5 ) ) ) 2 cos ( x ( 3 log 5 ) ) ( 3 log 5 ) x ( 3 log 5 1 ) \frac{d}{dx}f(x)=e^{(2\sin(x^{(3 \log 5)}))} * 2\cos(x^{(3 \log 5)}) * (3 \log 5) x^{(3 \log 5 - 1)}

Evaluating at x = 5 x=5 , being careful with entering the numbers in our calculator, we get an approximate answer of -6572.05.

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