解
a^2-3a+1=0
所以 a+1/a=3
(a+1/a)^2=a^2+2+1/a^2=9
a^2+1/a^2=7
a的4次方加1分之a的平方
=(a^2+1/a^2)-2a^2*1/a^2
=7^2-2
=47