8)
y = sin2x -√3cos2x + 4
Chia cả 2 vế cho 2 ta đc pt: sin(2x+π/3) +2
Ta có:
-1≤ sin(2x+π/3)≤ 1
-1+2 ≤ sin(2x + π/3)+2 ≤ 1+2
Vậy y min = 1 y max = 3
9) y = √3(cos²2x - sin²2x) + sin4x -3
√3cos4x + sin4x - 3
Chia cả hai vế cho 2
cos(4x - π/6) -3/2
Ta có
-1≤ cos(4x - π/6) ≤ 1
-5/2 ≤ cos(4x-π/6) -3/2 ≤ -1/2
Vậy y min = -5/2 y max = -1/2
