Question

谁会解这道题：已知x²-5x+1=0,求x²+1／x²的值。急需，谢谢！！！

Answer 1

用△判别式解，x²-5x+1=0
a=1,b=-5,c=1
△=b平方-4ac=21
x=-b±根号△
最后=5(5-√21）／2

Answer 2

x^2+1/x^2=(x^4+1)/x^2=(x^4++2x^2+1)/x^2-2=(x^2+1)^2/x^2-2=(5x)^2/x^2-2=23