2sin^2 2x – 5sin 2x – 7 = 0

Question

2sin^2 2x – 5sin 2x – 7 = 0

Answer 1

2*sin²(2x)-5*sin(2x)-7=0
sin(2x)=t   ⇒
2t²-5t-7=0   D=81
t₁=3.5 ∉
t₂=-1   sin(2x)=-1   2x=3π/2+2πn   x=3π/4+πn.