Question

(1/(1-ctg^2B))+(1/(tg^2B-1))=(1/(sin^2B-cos^2B))

Answer 1

(sina+cosa)^2=1/3^2
(sina)^2+2sinacosa+ (cosa)^2=1/9 (sina)^2+(cosa)^2=1 2sinacosa=sin2a
1+sin2a=1/9
sin2a=-8/9
Вроде так...))))