y=2-cos(2x-π/6)的值域x∈[π/6,3π/4]
x∈[π/6,3π/4]
则2x-π/6∈[π/6,4π/3]
通过余弦图像可以得到当2x-π/6=π即X=7π/12时cos(2x-π/6)得最小值-1,y得最大值3
当x=π/6或x=3π/4时cos(2x-π/6)得最大值( 根号3/2),即y得最小值 2-根号3/2
由此可得y的值域：y∈[2-根号3/2,3]
应该够详细了,