Please answer the following question 我只計到135 度, 為什麼還有一個答案325度 呢? 謝謝?

1 + 3sinθcosθ + 2sin²θ - 2sin⁴θ = 0

1 + 3sinθcosθ + 2sin²θ(1 - sin²θ) = 0

1 + 3sinθcosθ + 2sin²θcos²θ = 0

(1 + sinθcosθ)(1 + 2sinθcosθ) = 0

sinθcosθ = -1   or   sinθcosθ = -1/2

2sinθcosθ = -2   or   2sinθcosθ = -1

sin(2θ) = -2 (rejected)   or   sin(2θ) = -1
          where 0 ≤ 2θ < 4π (because 0 ≤ θ < 2π)

Therefore,

2θ = 3π/2 or 2θ = 2π + 3π/2 = 7π/2

θ = 3π/4 or 7π/4