5sin^2x-11cisx^2+3=0
5sin²x-11cos²x+3 = 0 5sin²x-11(1-sin²x)+3 = 0 5sin²x-11+11sin²x+3 = 0 16sin²x-8 = 0 16sin²x = 8 sin²x = 1/2 sin x = 1/√2 и sin x = -1/√2 sin x = 1/√2 → x = (-1)^n·π/4+πn sin x = -1/√2 → x = (-1)^n·5π/4+πn, n∈Z