Смотрим при каких значениях ч график выше 0
x∈(-∞;-3) U (2;∞)
<span>4sin²x + 12cosx-9=0</span>
<span>4-4cos²x+12cosx-9=0</span>
<span>t=cosx</span>
<span>4t²-12t+5=0</span>
<span>t=(12±√(144-80)/8=(12±8)/8</span>
<span>t₁=20/8, t₂=½</span>
<span>cosx=½ => x=±π/3+2πn</span>
<span>Xmin=π/3</span>