Question

Tga*ctga-cos^2a/2sina

Answer 1

$tg \alpha *ctg \alpha -cos^2 \alpha /sin2 \alpha =1- \frac{cos x^{2} \alpha }{2sin \alpha*cos \alpha }=1- \frac{cos \alpha }{2sin \alpha }=1- \frac{1}{2}ctg \alpha$