1/cos^2 х +3 tgx - 5 =0
1 + tg^2 x + 3 tgx - 5 =0
tg^2 + 3tgx - 4 =0
Пусть tgx=t, тогда
t^2 + 3t - 4=0
t1+t2 = -3
t1*t2 = -4
t1 = 1
t2 = -4
tgx = 1
x = pi/4
tgx = -4
x = - arctg4
