Question

ОЧЕНЬ СРОЧНО НУЖНО!!!!!!!

Answer 1

(sin^4 a - cos^4 a)/(1-cos a)(1+cos a) + 2 ctg^2 a - 1/sin^2 a =
(sin^2 a - cos^2 a)(sin^2 a+cos^2 a)/(1- cos^2 a) + 2cos^2 a/sin^2 s - 1/sin^2 a =
(sin^2 a - cos^2 a)*1/sin^2 a + 2cos^2 a/sin^2 s - 1/sin^2 a = 
=(sin^2 a - cos^2 a + 2cos^2 - 1)/sin^2 a = (sin^2 a+cos^2 a -1)/sin^2 a=
=(1-1)/sin^2 a = 0

Answer 2

Решение на фотографии.