(1)因为sin x/2=2cos x/2 所以tanx/2=(sin x/2)/(cos x/2)=2所以tanx=[2tan(x/2)]/[1-tan^2(x/2)]=-4/3(2)原式=[cos^2x-sin^2x]/[(cosx-sinx)*sinx]=(cosx-sinx)(cosx+sinx)/(cosx-sinx)*sinx=(cosx+sinx)/sinx=cotx...