Question

Доказать тождество $\frac{cos^{2}a-sin^{2}a }{sina cosa} = \frac{1-tg^{2}a }{tga}$

Answer 1

$\frac{1-tg^2\alpha }{tg\alpha } =\frac{1-\frac{sin^2\alpha }{cos^2\alpha } }{\frac{sin\alpha }{cos\alpha } } =\frac{\frac{cos^2\alpha-sin^2\alpha }{cos^2\alpha } }{\frac{sin\alpha }{cos\alpha } } =\frac{cos^2\alpha -sin^2\alpha }{sin\alpha\cdot cos\alpha }$