Выражение: а) -tgа x ctga + cos^2a б) sin^2a/1-cos^2a

A)-tg(а)*ctg(a) + cos^2(a) = - (tgа*ctga) + cos^2 a = -1+cos^2 (a)=-1+(1-sin^2 (a))= -1+1-sin^2 (a)=-sin^2 (a)

б) sin^2(a)/(1-cos^2(a)) = sin^2(a)/(sin^2(a)) = 1