a^2+3a+1=0,
显然a不等于0
所以两边除以a
a+3+1/a=0
a+1/a=-3
两边平方
a^2+2+1/a^2=9
a^2+1/a^2=7
a^2/a^4+1
上下同除以a^2
=1/(a^2+1/a^2)
=1/7