7sin2x-22cos^2x+10=0
14sinxcosx - 22cos^2x + 10(sin^2x + cos^2x) = 0
14sinxcosx -12cos^2x +10sin^2x = 0 |:cos^2x
14tgx - 12 + 10tg^2x = 0
5tg^2x +7tgx - 6 = 0
tgx = t
5t^2 +7t - 6 = 0
D = 49 + 4*5*6 = 169
t = (-7 +- 13)/10
t = -2 t = 3/5
tgx = -2 tgx = 3/5
x = -arctg2 + Пk x = arctg(3/5) + Пk