f(x)=xcosx,f'(x)是它的导函数,求f'(4/π)的值

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f(x)=xcosx,f'(x)是它的导函数,求f'(4/π)的值
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f(x)=xcosx,f'(x)是它的导函数,求f'(4/π)的值
f(x)=xcosx,f'(x)是它的导函数,求f'(4/π)的值

f(x)=xcosx,f'(x)是它的导函数,求f'(4/π)的值
f'(x)=x'cosx+x(cosx)'=cosx-xsinx
f'(π/4)=cos(π/4)-(π/4)sin(π/4)=(√2/2)(1-π/4)

f'(x)=x'*cosx+x*(cosx)'=cosx-xsinx
f'(4/π)=cos(π/4)-(π/4)*sin(π/4)=(√2/2)*(1-π/4)