谁能证明 :tan(x+90)=-cotx
问题描述:
谁能证明 :tan(x+90)=-cotx
答
tan(x+90)=-tan(180-x-90)=-tan(90-x)=-cotx
答
tan(x+90)=sin(x+90)/cos(x+90)=cos x/-sin x[根据诱导公式],-(cos x/sin x)=-cot x
答
sin(x+90)=cosxsin90+sinxcos90=cosx+0=cosx
cos(x+90)=cosxcos90-sinxsin90=0-sinx=-sinx
tan(x+90)=sin(x+90)/cos(x+90)=cosx/(-sinx)=-cotx
够详细了吧?