a是方程x平方-3x+1=0的根,
则a²-3a+1=0
则a²+1=3a
两边同时除以a,得a+1/a=3
a²=3a-1
则
2a平方-5a-2+3/a平方+1
=2(3a-1)-5a-2+3/3a
=6a-2-5a-2+1/a
=-4+a+1/a
=-4+3
=-1