log2（3）=x
2^x=3
（2^(2x)-2^(-2x))/(2^(x)-2^(-x))
=[(2^x)^2-1/(2^x)^2]/[2^x-1/2^x]
=[(2^x+1/2^x)(2^x-1/2^x)]/[2^x-1/2^x]
=2^x+1/2^x
=3+1/3
=10/3