设a、b是方程:x²-3x+1=0的两个根.
则有:a²-3a+1=0
b²-3b+1=0
a+b=3
ab=1
∴ a/b+b/a=﹙a²+b²﹚/ab
=a²+b²
=﹙a+b﹚²-2ab
=3²-2
=7.