Question

помогитеееееееее!!!!!​

Answer 1

$\displaystyle ctg^2\alpha -cos^2\alpha =\frac{cos^2\alpha }{sin^2\alpha }-cos^2\alpha = \frac{cos^2\alpha -cos^2\alpha *sin^2\alpha }{sin^2\alpha }=\frac{cos^2\alpha*(1-sin^2\alpha ) }{sin^2\alpha }=\frac{cos^2\alpha*cos^2\alpha }{sin^2\alpha }=\frac{cos^4\alpha }{sin^2\alpha }=ctg^2\alpha *cos^2\alpha$