Стригонометрическим уравнением: 2sin^2x-7cos2x-5=0

2sin^2x - 7(1 - 2sin^2x) - 5 = 0 
2sin^2x - 7 + 14sin^2x - 5 = 0 
16sin^2x - 12 = 0 
sin^2x = 3/4
sinx = ± √3/2

1) sinx = √3/2
x = pi/3 + 2pik, k ∈Z
x = 2pi/3 + 2pik, k ∈Z

2) sinx = - √3/2
x = - pi/3 + 2pik, k ∈Z
x = 4pi/3 + 2pik, k∈ Z

2sin²x-7+14sin²x-5=0
16sin²x=12
sin²x=3/4
(1-cos2x)/2=3/4
1-cos2x=1,5
cos2x=-0,5
2x=+-2π/3+2πn,n∈z
x=+-π/3+πn,n∈z