AP Calculus ABeasymcq1 pt

If f(x)=cos(3x)f(x)=\cos(3x), then f(x)=f'(x)=

A.3sin(3x)3\sin(3x)
B.3sin(3x)-3\sin(3x)
C.sin(3x)-\sin(3x)
D.3sinx-3\sin x

Explanation

Core Concept

The chain rule gives cos(3x)3\cos'(3x)\cdot 3. Since cosu=sinu\cos' u=-\sin u, the result is 3sin(3x)-3\sin(3x).

Correct Answer

B3sin(3x)-3\sin(3x)

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