Решите уравнение sin^2x-cos2x=0.5 найдите все решение на промежутке [-(7п)/2; -2п]

Sin²x-cos2x=1/2
(1-cos2x)/2-cos2x=1/2
1-cos2x-2cos2x=1
-3cos2x=0
cos2x=0
2x=π/2+πn,n∈z
x=π/4+πn/2,n∈z
-7π/2≤π/4+πn/2≤-2π
-14≤1+2n≤-8
-15≤2n≤-9
-7,5≤n≤-4,5
n=-7⇒x=π/4-7π/2=-13π/2
n=-6⇒x=π/4-3π=-11π/4
n=-5⇒x=π/4-5π/2=-9π/4