a^2-3a+1=0
a+1/a=3
(a+1/a)^2=3^2=9
(a+1/a)^2=a^2+1/a^2+2=9
a^2+1/a^2=9-2=7
(a^2+1/a^2)^2=a^4+1/a^4+2=49
a^4+1/a^4=49-2=47a^2-3a+1=0到a+1/a=3是怎吗来的a^2-3a+1=0等式两边同时除以a，得：a-3+1/a=0a+1/a=3