Question

y=e^-xcos2x求导

Answer 1

y′＝［e^（－x）］′cos2x＋e^（－x）（cos2x）′
＝e^（－x）（－x）′cos2x－e^（－x）sin2x（2x）′
＝－e^（－x）cos2x－2e^（－x）sin2x.