2^x=3
则x=log2(3)
y=log4(8/3)=lg(8/3)/lg4
=lg(8/3)/2lg2
所以2y==lg(8/3)/lg2=log2(8/3)
所以x+2y
=log2(3)+log2(8/3)
=log2(3×8/3)
=log2(8)
=3