Sin^2a-4sin^a/sin^2a-4+4sin4a

1) sin²2a-4sin²a=4sin²acos²a-4sin²a=4sin²a (cos²a-1) = 4sin²a * (-sin²a) =

=-4sin^4a

2) sin²2a-4+4sin^4a=sin²2a-4 (1-sin^4) a=sin²2a-4 (1-sin²a) (1+sin²a) =

=4sin²acos²a-4*cos²a * (1+sin²a) = 4sin²acos²a-4cos²a-4cos²asin²a=-4cos²a

3) - 4sin^4a / (-4cos²a) = tg²a*sin²a