50 тригонометрия, выражение sin^2((pi/2)+а)-cos^4(pi-a)+cos^4((3pi/2)-a)

Sin((pi/2)+А) = cos(А)
cos(pi-A) = -cos(A)
cos((3pi/2)-A) = -sin(A)
... = cos^2(А) - cos^4(А) + sin^4(A) =
= cos^2(A) + (sin^2(A) - cos^2(A))(sin^2(A) + cos^2(A)) =
= cos^2(A) + sin^2(A) - cos^2(A) = sin^2(A)