设a:b=c:d=e:f=2:3 =k,则a=(2/3)b,c=(2/3)d,e=(2/3)f,代入得原式等于
（(2/3)b+2*(2/3)d-3*(2/3)f)):(b+2d-3f)=2/3
也可直接利用等比定理,a:b=2c:2d=3e:3f=2:3,(a+2c-3e):(b+2d-3f)=2/3