Question

Доказать тождество
$frac{sin2a-2cosa}{sina-sin^{2}a} =-2ctga$

Answer 1

$frac{sin2a-2cosa}{sina-sin^{2}a} =-2ctga\\ frac{2sinacosa-2cosa}{sina(1-sina)} = frac{-2cos(1-sina)}{sina(1-sina)}=-2 frac{cosa}{sina}=-2ctga$