x^2-5x+1=0
x=[5±√(25-4)]/2=(5±√21)/2
x1=(5+√21)/2,x2=(5-√21)/2
补充答案:
因为:x1=(5+√21)/2,x2=(5-√21)/2
所以:
(x1)^2=(25+21+10√21)/4=(23+5√21)/2
(x2)^2=(25+21-10√21)/4=(23-5√21)/2
代入所求,有:
①:x^2+1/(x^2)
=(23+5√21)/2+2/(23+5√21)
=[(23+5√21)^2+4]/[2(23+5√21)]
=(529+525+230√21+4)/[2(23+5√21)]
=(529+115√21)/(23+5√21)
=(529+115√21)(23-5√21)/(23+5√21)(23-5√21)
=92/4
=23
②:x^2+1/(x^2)
=(23-5√21)/2+2/(23-5√21)
={[(23-5√21)^2]+4}//[2(23-5√21)]
=(529-115√21)/(23-5√21)
=(529-115√21)(23+5√21)/[(23+5√21)(23-5√21)]
=92/(529-525)
=23
所以:x^2+1/(x^2)=23