因为4a-1/(a+2)(a-1)=m/(a+2) + n/(a-1),
所以4a-1/(a+2)(a-1)=((m+n)a-m+2n)/(a+2)(a-1)
4a-1=(m+n)a-m+2n
m+n=4,-m+2n=-1.
故m=3,n=1.