x^2-3x+1=0两边除以x得x-3+1/x=0∴x+1/x=3两边平方得x²+2+1/x²=9∴x²+1/x²=7
x^2-3x+1=0 等式两边同时除以xx-3+1/x=0x+1/x=3x^2+1/x^2=(x+1/x)^2-2=3^2-2=9-2=7
