f（x）=1/4^x-1/2^x+1=(1/2^x-1/2)^2+3/4
-3≤x≤2,1/8≤2^x≤4,1/4≤1/2^x≤8
f(x)min=3/4
f(x)max=(8-1/2)^2+3/4=57