Question

Подскажите как это решить?

Answer 1

$sin^2alpha+cos^2alpha+operator{tg}^2beta=1+operator{tg}^2beta=frac{1}{cos^2beta};$

$frac{tg alpha}{ctg alpha}(1-sin^2 alpha)= frac{tg alpha}{ frac{1}{tg alpha}}cdotcos^2=tg^2 alphacdotcos^2 alpha=frac{sin^2 alpha}{cos^2 alpha} cdotcos^2 alpha=sin^2 alpha$