8sin²x + 2sinxcosx - 6cos²x = 0

Разделив на cos^2x, получим 8tg^2x + 2tgx - 6 = 0 |:2 4tg^2x + tgx - 3 = 0 D=b^2-4ac = 1 + 4 * 4 * 3 = 49 tgx = (-1+7)/8 = 3/4 x1 = arctg(3/4) + pi*n tgx = (-1-7)/8 = -1 x2 = -pi/4 + pin