Question

син^2(7пи/2-а) +син^2(6пи+а)

Answer 1

7π/2=2·2π+3π/2
6π=3·2π
  sin²(7π/2-α) = sin²(3π/2 -α) =cos²α
  sin²(3·2π+α) = sin²α
 cos²α+sin²α= 1