erzhan9210 1) tg²A-sin²A=sin²a/cos²a-sin²a= (sin²a-sin²a*cos²a)/cos²a = [sin²a(1-cos²a)]/cos²a= (sin²a*sin²a)/cos²a = sin⁴a/cos²a
2) 1/sin²a-1 = (1-sin²a)/sin²a = cos²a/sin²a
3) sin⁴a/cos²a*cos²a/sin²a= sin²a