Sin2x+2cos2x=0 2sinxcos + 2cos^2x - 2sin^2x = 0 | : cos^2x -2tg^2x + 2tgx + 2 = 0 | : 2 -tg^2x + tgx + 1 = 0 D = 1 - 4 * -1 D = 5