4sin²x + 12cosx-9=04-4cos²x+12cosx-9=0t=cosx4t²-12t+5=0t=(12±√(144-80)/8=(12±8)/8t₁=20/8, t₂=½cosx=½ => x=±π/3+2πnXmin=π/3
4sin²x + 12cosx-9=0
4-4cos²x+12cosx-9=0
t=cosx
4t²-12t+5=0
t=(12±√(144-80)/8=(12±8)/8
t₁=20/8, t₂=½
cosx=½ => x=±π/3+2πn
Xmin=π/3