Question

Как доказать тождество (ctg t )/(tg t+ctg t) = cos^2 t

Answer 1

$\frac{ctgt}{tgt+ctgt} = \frac{\frac{cost}{sint}}{\frac{sint}{cost}+\frac{cost}{sint}} = \frac{cost}{sint\cdot \frac{sin^2t+cos^2t}{sint\cdot cost}} = \frac{cost}{\frac{1}{cost}} =cos^2t$