Problemddx(xcosx)\frac{d}{dx}(x \cos x)dxd(xcosx)Step-by-step solution套用 (fg)′=f′g+fg′(fg)' = f'g + fg'(fg)′=f′g+fg′，其中 f=xf = xf=x、g=cosxg = \cos xg=cosx。f′=1f' = 1f′=1，g′=−sinxg' = -\sin xg′=−sinx。結果：cosx−xsinx\cos x - x\sin xcosx−xsinx。Answercos(x)−xsin(x)\cos(x) - x\sin(x)cos(x)−xsin(x)Want to solve a different problem? Open the derivative solver →Related worked examples/solve/calculus/derivative-of-cos-xRead more/blog/chain-rule-mastery