2sin^2x + sinxcosx - 3cos^2x = 0 | :cos^2x (cos^2x <> 0)
2tg^2x + tgx - 3 = 0
(2tgx + 3)(tgx - 1) = 0
1. tgx - 1 = 0 -> tgx = 1 -> x = П/4 + Пk = {x на отрезке [П/2; 3П/2]} = 5П/4
2. 2tgx + 3 = 0 -> tgx = -3/2 -> x = -arctg(3/2) + Пk = {-||-} = П - arctg(3/2)
x = {5П/4, П - arctg(3/2)}