/ 是分数线,分数线左边为分子、右边为分母
m/(m²-6m+9)=m/(m-3)²
-3m/(2m²-18)=-3m/[2(m²-9)]=-3m/[2(m+3)(m-3)]
1/(2m+6)=1/[2(m+3)]
以上三个分式的最简公分母是2(m+3)(m-3)²
m/(m-3)²=[m×2(m+3)]/[2(m+3)(m-3)²]=[2m(m+3)]/[2(m+3)(m-3)²]
-3m/[2(m+3)(m-3)]=[-3m(m-3)]/[2(m+3)(m-3)²]
1/[2(m+3)]=(m-3)²/[2(m+3)(m-3)²]