log7(2cos²x + 3cos x - 1) = 0
log7(2cos²x+3cosx-1) = log7(1)
2cos²x+3cosx-1 = 1
2cos²x+3cosx-2 = 0
cos²x+3/2cos x - 1 = 0
Теорема Виета:
{cos x1 + cos x2 = -3/2
{cosx1•cosx2 = -1
cos x1 = -2
cos x2 = 1/2
1)cos x = -2
∅, min(cos x) = -1
2)cos x = 1/2
x = ±π/3 + 2πk, k€Z
