Question

Доказать тождество.........................

Answer 1

$\frac{cos^{2}x}{1-cos^{2}x} = \frac{cos^{2}x}{sin^{2}x} = (\frac{cosx}{sinx})^{2}=ctg^{2}x$

Answer 2

$\frac{cos ^{2} x}{1-cos ^{2} x} = \frac{cos ^{2} x}{sin ^{2} x} =ctg ^{2} x$