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

(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...))))