∵x∈[-π/3,π/6] ∴2x+π/3∈[-π/3,2π/3]
∴cos（2x+π／3)∈[-1/2,1]
∵f(x)值域为[-1,5]
当a>0时,
cos(2x+π/3)=1时,f(x)max=3a/2+b=5
cos(2x+π/3)=-1/2时,f(x)min=b=-1
∴a=4,b=-1
当a