29. 5 sin 2x (1 + cos 2x) = 4 cos² x.

2sin x cos x (1 + 2cos² x - 1) = 4 cos² x, 2sin x cos x * 2cos² x = 4 cos² x, 4sin x cos³ x - 4 cos² x = 0, 4cos² x(sin x cos x - 1) = 0, cos x = 0, x = π/2 + πn. n ∈ Z