Question

Помогите решить ctgasin2a-cos2a

Answer 1

$Ctg \alpha Sin2 \alpha -Cos2 \alpha = \frac{Cos \alpha }{Sin \alpha }*2Sin \alpha Cos \alpha -Cos2 \alpha=2Cos ^{2} \alpha -$$(2Cos ^{2} \alpha -1)=2Cos ^{2} \alpha -2Cos ^{2} \alpha +1=1$

Answer 2

$ctg a\sin 2a-\cos 2a=\frac{\sin 2a\cdot \cos a-\cos 2a\cdot \sin a}{\sin a}= \frac{\sin(2a-a)}{\sin a}=\frac{\sin a}{\sin a}=1$