sin3x + cos3x = 0 /: cos3x≠0
tg3x + 1 = 0
tg3x = - 1
3x = - arctg(1) + pik
3x = - pi/4 + pik /:3
x = - pi/12 + pik/3, k ∈ Z
0 ≤ - pi/12 + (pi/3)*k ≤ 6
0 ≤ - 0,26 + (1,05)*k ≤ 6 / + 0,26
0, 26 ≤ (1,05)*k ≤ 6, 26 / : 1,05
0,25 ≤ k ≤ 5,96
k = 1, 2, 3, 4, 5
k = 1 ===> x = - pi/12 + 4pi/12 = pi/4
k = 2 ===> x = - pi/12 + 8pi/12 = 7pi/12
k = 3 ==> x = - pi/12 + 12pi/12 = 11pi/12
k = 4 ===> x = - pi/12 + 16pi/12 = 5pi/4
k = 5 ===> x = - pi/12 + 20pi/12 = 19pi/12