(1/sina+ctga)*(1/sina-ctga)

Question

(1/sina+ctga)*(1/sina-ctga)

Answer 1

По формуле (a-b)*(a+b) = a^2 - b^2 получаем:

1/sin^2a - ctg^2a = ct^2a - ct^2a = 0

*1/sin^2 = ctg^2