（1）2/x=3/(x+1)
2(x+1)=3x
2x+2=3x
x=2
(2)1/(x-4)=8/(x^2-16)
8(x-4)=x^2-16=(x+4)(x-4)
(x-4)(x+4-8)=0
(x-4)^2=0
x-4=0
x=4
帶入檢驗,x=4使得分母x-4和x^2-16等于0
不成立
所以原方程無解
12/(m^2-9)+2/(3-m)
=12/(m^2-9)-2/(m-3)
=12/(m^2-9)-2(m+3)/(m-3)(m+3)
=(12-2m-6)/(m-3)(m+3)
=(6-2m)/(m-3)(m+3)
=2(m-3)/(m-3)(m+3)
=2/(m+3)