2x²-5x+1=0的两根是x1,x2
则 x1+x2=5/2
x1x2=1/2
则1/x1+1/x2
=(x1+x2)/x1x2
=5
1/x1*1/x2
=1/x1x2
=2
所以方程是x²-5x+2=0