а) 2sin2x-1 = 0, sin2x = 1/2
2x = (-1)^n*arcsin1/2 + πn
2x = (-1)^n *π/6 + πn
x = (-1)^n* π/12 + πn/2
б) cos²x - cosx = 0
cosx(cosx-1) = 0
б.1) cosx = 0
x = π/2 + πn
б.2) cosx -1 = 0
cosx = 1
x = 2πn
