当x等于多少时,分式x2-1/x+1的值为零.化简12/m2-9+2/m+3的结果是?
问题描述：
当x等于多少时,分式x2-1/x+1的值为零.化简12/m2-9+2/m+3的结果是?
答
做法一：1、因为x2-1=（x+1)(x-1)=0，且x+1≠0 所以，x-1=0 x=1
2、12/(m2－9)+2/m+3
=12/(m+3)(m-3)+2/(m+3)
=(12+2m-6)/(m+3)(m-3)
=2(m+3)/(m+3)(m-3)
=2/(m-3)
做法二：(1)x^2-1=0且x+1不等于0，所以：x=1
(2)12/(m^2-9)+2/(m+3)==[12+2(m-3)]/[(m+3)(m-3)]=(2m+6)/[(m+3)(m-3)]=2/(m-3)
答
1、因为x2-1=（x+1)(x-1)=0，且x+1≠0 所以，x-1=0 x=1
2、12/(m2－9)+2/m+3
=12/(m+3)(m-3)+2/(m+3)
=(12+2m-6)/(m+3)(m-3)
=2(m+3)/(m+3)(m-3)
=2/(m-3)
答
(1)x^2-1=0且x+1不等于0,所以：x=1
(2)12/(m^2-9)+2/(m+3)==[12+2(m-3)]/[(m+3)(m-3)]=(2m+6)/[(m+3)(m-3)]=2/(m-3)