已知6x/(x^2-9)=m/(x+3)+n/(n-3)求常数m,n的值
问题描述：
已知6x/(x^2-9)=m/(x+3)+n/(n-3)求常数m,n的值
答
6x/(x^2-9)=m/(x+3)+n/(x-3)
6x/(x+3)(x-3)=(mx-3m+nx+3n)/(x+3)(x-3)
∴6x=x(m+n)-3(m-n)
m+n=6
m-n=0
∴m=3
n=3