是y=4^(x-1/2)-3×2^x+5吧，y=4^(x-1/2)-3×2^x+5=4^x*(1/2)-3*2^x+5,令2^x=t,y=(1/2)t^2-3t+5,=(1/2(t-3)^2+1/2,因为01
