Question

急！！数学题！！！

已知x+ 1/x =3，求x^2 + 1/x^2 的值
注意：1/x^2 的意思是x的二次方分之一

Answer 1

（x+ 1/x）^2=9
（x+ 1/x）^2
=x^2 + 1/x^2+2
=9

x^2 + 1/x^2
=9-2
=7

Answer 2

7

Answer 3

x^2 + 1/x^2=(x+ 1/x)^2-2=7

Answer 4

因为 X+1/X=3
所以（X+1/X)^2= X^2+1/X^2+2=9
所有 X^2+1/X^2=7

Answer 5

（x+ 1/x）^2=x^2+2x1/x+1/x^2=9 x^2 + 1/x^2=9-2=7

Answer 6

(x+ 1/x )^2=x^2 + 1/x^2 +2=9,故x^2 + 1/x^2 =7