forever2003jan
幼苗
共回答了18个问题采纳率:100% 举报
原式
=2n/(m+2n)-m/(m-2n)-4mn/(m²-4n²)
=2n/(m+2n)-m/(m-2n)-4mn/(m²-4n²)
=[2n(m-2n)-m(m+2n)-4mn]/(m²-4n²)
=(2mn-4n²-m²-2mn-4mn)/(m²-4n²)
=(-4n²-m²-4mn)/(m²-4n²)
=-(m+2n)²/[(m+2n)(m-2n)]
=-(m+2n)/(m-2n)
m=1/5n,则n=5m,于是
原式
=-(m+10m)/(m-10m)
=-11m/(-9m)
=11/9
答题不易,谢谢
1年前
4