(1x3x4+2x6x8+.+nx3nx4n)/(1x4x5+2x8x10+.+nx4nx5n)
=(1x3x4x(1+2+3+……+ n))/(1x4x5x(1+2+3+……+ n))
=(1x3x4x)/(1x4x5x)
=3/5
(1乘4乘5+2乘8乘10+.+n乘4n乘5n)分之(1乘3乘4+2乘6乘8+.+n乘3n乘4n)
=(1乘4乘5乘(1+2+3+……+ n))分之(1乘3乘4乘(1+2+3+……+ n))
=(1乘4乘5乘)分之(1乘3乘4乘)
=5分之3