Question

Выражение: а) cos 2 a/cos a-sin a б)cos2 b+sin^2 b в)sin b/2 cos^2 b/2

Answer 1

А)
$\frac{cos2 \alpha }{cos \alpha -sin \alpha } = \frac{cos^2 \alpha -sin^2 \alpha }{cos \alpha -sin \alpha } = \frac{(cos \alpha -sin \alpha )(cos \alpha +sin \alpha )}{(cos \alpha -sin \alpha )} =cos \alpha +sin \alpha$
б)
$cos2 \beta +sin^2 \beta =cos^2 \beta -sin ^2\beta +sin^2 \beta =cos^2 \beta$