x^2n=3
所以：x^n=√3.
(2x)^3n/(4x)^4n
=(2^3n*x^3n)/(4^4n*x^4n)
=[(2^3n)/(2^8n)]*[x^3n/x^4n)
=(1/2^5n)*(1/x^n)
=1/(√3*2^5n).