问题 选择题 函数y=sinxcosx的导数为( )A.cos2x-sin2xcos2xB.-cos2x+sin2xcos2xC.cos2x+sin2xcos2xD.-cos2x-sin2xcos2x 答案 ∵y′=(sinxcosx)′=cos2x-sinx(-sinx)cos2x=cos2x+sin2xcos2x=1cos2x,故选C.