应该是a^2-3a+1=0
a^2-3a+1=0
等式两边同除以a
a-3+1/a=0
a+1/a=3
a^2+1/a^2=(a+1/a)^2-2=3^2-2=7
(a-1/a)^2=(a+1/a)^2-4=3^2-4=5已知x+y=1,xy=1/5,求(x^2+1)(y^2+1)，要过程(x^2+1)(y^2+1)=x^2y^2+x^2+y^2+1=(xy)^2+(x+y)^2-2xy+1=(1/5)^2+1^2-2/5+1=1/25+1-2/5+1=41/25