Нужно дробь: (4cos^2(2a)-4cos^2(a)+3sin^2(a))/(4sin^2(a)-sin^2(2a))

(4cos^2(2a)-4cos^2(a)+3sin^2(a))/(4sin^2(a)-sin^2(2a))=
=(4cos²a-4sin²a-4cos²a+3sin²a)/(4sin²a-4sin²acos²a)=
=-sin²a/[4sin²a(1-cos²a)]=-1/4sin²a