1+sinα/cosα=-1/2则(1+sinα)(1-sinα)/[cosα(1-sinα)]=-1/2则(1-sin²α)/[cosα(1-sinα)]=-1/2则cos²α/[cosα(1-sinα)]=-1/2则cosα/(1-sinα)=-1/2则cosα/(sinα-1)=1/2
因为1+sinα/cosα=-1/2,所以sinα/cosα=-3/2,那么cosα/sinα=-2/3所以cosα/sinα-1=-5/3
负3分之5