15xy/世纯念(6x-3y)-(2x-y)/10xy=15xy/3(2x-y)-(2x-y)/(5xy*2)=2-1/4=7/4由题意得n+2=3,2m-3=1解得n=1,m=2xy不等于0,所裤灶以搜困2a+5b=0所以代数式等于0