Question

Спростіть вираз (2tg^2a/1-cos2a)- 1/ctg^2a

Answer 1

$\frac{2tg^2x}{1-cos2x}-\frac{1}{ctg^2x}=\frac{2sin^2x}{cos^2x\cdot 2sin^2x}-\frac{sin^2x}{cos^2x}=\frac{1}{cos^2x}-\frac{sin^2x}{cos^2x}=\\\\= \frac{1-sin^2x}{cos^2x}= \frac{cos^2x}{cos^2x}=1\\\\\\P.S.\quad sin^2x=\frac{1-cos2x}{2}\quad \to \quad 1-cos2x=2sin^2x$