谁告诉我这道数学怎么解

1/(x-3)＋k/(x＋3)=3＋k/(x^2-9)
x+3/(x^2-9)+k(x-3)/(x^2-9)=3+k/(x^2-9)
x+3+kx-3k-3-k/(x^2-9)-3+k/(x^2-9)=0
x+3+kx-3k-3-k/(x^2-9)=0
x+kx-4k/(x^2-9)=0
x+kx-4k=0
因为x=3或x=-3是增根,所以,
当x=3时,3+3k-4k=0
3-k=0
k=3
当x=-3时,-3-3k-4k=0
-3=7k
k=-3/7
所以k=3或k=-3/7

把分母的括号添上,