Question

ctgx-ctg2x=1/sin2x доказать

Answer 1

$ctgx-ctg2x= frac{cosx}{sinx} - frac{cos2x}{sin2x} = frac{sin2xcdot cosx-cos2xcdot sinx}{sinxcdot sin2x} =\\= frac{sin(2x-x)}{sinxcdot sin2x} = frac{sinx}{sinxcdot sin2x} = frac{1}{sin2x}$