a²-3a+1=0
等式两边同除以a
a-3+1/a=0
a+1/a=3
a⁴+1/a⁴=(a²+1/a²)²-2
=[(a+1/a)²-2]²-2
=(3²-2)²-2
=(9-2)²-2
=7²-2
=49-2
=47