1.
m/(x-2)+n/(x+1)=(x-8)/[(x+1)(x-2)]
m(x+1)+n(x-2)=(x-8)
mx+m+nx-2n=x-8
(m+n)x+(m-2n)=x-8
m+n=1
m-2n=-8
解方程组：
m=-2,n=3
2.
x^2-4x+1=0
x-4+1/x=0
x+1/x=4
x^2+1/x^2=(x+1/x)^2-2=16-2=14
^2平方