36.
cos4xcos5x + sin4xsin5x = √3/2
cos(5x - 4x) = √3/2
cosx = √3/2
x = π/6 + 2πn
x = -π/6 + 2πn
n ∈ Z
37.
2sin²x + 7sinxcosx - 9cos²x = 0 | :cos²x
2tg²x + 7tgx - 9 = 0
tgx = t
2t² + 7t - 9 = 0
t = -4.5
t = 1
tgx = -4.5
tgx = 1
x = -arctg(4.5) + πn
x = π/4 + πn
n ∈ Z