已知x在[1,8],求y=[(log2^x)^2]-log4^x+3的值域
问题描述：
已知x在[1,8],求y=[(log2^x)^2]-log4^x+3的值域
答
[(log2^x)^2]-log4^x+3
=[(log2^x)^2]-2log2^x+3
= [(log2^x)-1]^2+2
min y = y(1)=(log2 -1)^2+2
max y = y(8)=(8log2-1)^2+2
值域 =[(log2 -1)^2+2,(8log2-1)^2+2]