Question

Доказать тождество :

Answer 1

$frac{ctga}{tga+ctga} = frac{frac{cosa}{sina}}{ frac{sina}{cosa} + frac{cosa}{sina} } = frac{cosa}{sina, cdot frac{sin^2a+cos^2a}{sinacdot cosa} }= frac{cosacdot sinacdot cosa}{sinacdot 1} =cos^2a$