若m/(x+4)-n/(x-4)=6x/(x^2-16),求mn的值
问题描述：
若m/(x+4)-n/(x-4)=6x/(x^2-16),求mn的值
答
m/(x+4)-n/(x-4)
=[m(x-4)-n(x+4)]/(x^2-16)
=[(m-n)x-4(m+n)]/(x^2-16)
m-n=6m+n=0
解得：
m=3 n=-3
mn=3×（-3）=-9