Question

Срочно! Помогите!!
$\frac{sin2a}{(sina+cosa)^2-1 }-sin^2a-cos^2a$

Answer 1

$\displaystyle \frac{\sin2 \alpha }{(\sin \alpha+\cos \alpha)^2-1 } -\sin^2 \alpha-\cos^2 \alpha=\\ \\ \\ = \frac{\sin2 \alpha}{1+\sin2 \alpha-1} -(\underbrace{\sin^2 \alpha+\cos^2 \alpha}_{1})=1-1=0$