Question

(1-sina)(1+sina)/cosa,

Answer 1

Ответ:

$\frac{(1 - \sin( \alpha ))(1 + \sin( \alpha )) }{ \cos( \alpha ) } = \frac{1 - \sin {}^{2} ( \alpha ) }{ \cos( \alpha ) } = \\ = \frac{ \cos {}^{2} ( \alpha ) }{ \cos( \alpha ) } = \cos( \alpha )$