Решение
3cos³x - 7cos²xsinx + 4sin³x = 0 делим на cos³x ≠ 0
4 tg³x - 7tgx + 3 = 0
tgx = t
4t³ - 7t + 3 = 0
t₁ = 1
4t³ - 7t + 3 It - 1I
-(4t³ - 4t²) 4t² + 4t - 3
4t² - 7t
-(4t² - 4t)
- 3t + 3
-( -3t + 3)
0
4t³ - 7t + 3 = (t - 1)*(4t² + 4t - 3)
4t² + 4t - 3 = 0
D = 16 + 4*4*3 = 64
t = (- 4 - 8)/8
t₂ = - 1,5
t = (- 4 + 8)/8
t₃ = 0,5
1) tgx = 1
x₁ = π/4 + πm, m∈Z
2) tgx = - 1,5
x₂ = - arctg1,5 + πk, k∈Z
3) tgx = 1/2
x₃ = arctg(1/2) + πn, n∈ Z