Question

Доказать тождество 5)

Answer 1

$frac{1}{1+tg^2 alpha } +sin^2 alpha = frac{1}{1+ frac{sin^2 alpha }{cos^2 alpha } } +sin^2 alpha =frac{1}{frac{cos^2 alpha +sin^2 alpha }{cos^2 alpha } } +sin^2 alpha = \ =frac{cos^2 alpha }{cos^2 alpha +sin^2 alpha } +sin^2 alpha = cos^2 alpha +sin^2 alpha =1$