Question

в ) помогите плииз упростить

Answer 1

Т.к. ctgA = cosA/sinA и sin²a + cos²a = 1, то
4/sin²a - 4ctg²a = 4/sin²a - 4cos²a/sin²a = (4 - 4cos²a)/sin²a = 4sin²a/sin²a = 4.