把a代入方程得
a²-3a+1=0 乘以3
3a²-9a+3=0
3a²-5a+3-4a=0
3a²-5a+3=4a
a²-3a+1=0
a²+1=3a
3a²-5a+3/a²+1
=4a/a²+1
=4a/3a
=4/3