计算 12/ m²-9 + 2/3-m
问题描述：
计算 12/ m²-9 + 2/3-m
答
解
12/(m²-9)+2/(3-m)
=12/(m-3)(m+3)-2(m+3)/(m-3)(m+3)
=(12-2m-6)/(m+3)(m-3)
=(-2m+6)/(m+3)(m-3)
=-2(m-3)/(m+3)(m-3)
=-2/(m+3)