若m+n=6,mn=2.75,则m-n
问题描述：
若m+n=6,mn=2.75,则m-n
答
(m+n)²=6²
m²+n²+2mn=36
m²+n²=36-2mn=36-5.5=30.5
(m-n)²
=m²+n²-2mn
=30.5-5.5
=25
所以m-n=-5或m-n=5