1)
1/4 tgx = 0 | :1/4
tgx = 0
x = pi/4 + pik, k ∈ Z
2)
sinx + cosx = 0 |:cosx ≠ 0⇒ x ≠ pi/2 +pik, k ∈ Z
tgx + 1 = 0
tgx = -1
x = -pi/4 + pik, k ∈ Z
3)
2cos3x + 1 = 0
2 cos3x = -1
cos3x = -1/2
3x = +- ( pi - pi/3) + 2pik
3x = +- 2pi/3 + 2pik
x = +-2pi/9 + 2pik/3, k ∈ Z
