初一数学,要详细过程,谢谢已知x-1/x=4,求下列各式的值:(1)x^2+1/x^2; (1)16x^2/(x^4-10x+1)

问题描述:

初一数学,要详细过程,谢谢
已知x-1/x=4,求下列各式的值:(1)x^2+1/x^2; (1)16x^2/(x^4-10x+1)

(1) x-1/x=4
(x-1/x)^2=16
x^2-2+1/x^2=16
x^2+1/x^2=16+2
x^2+1/x^2=18

  1. (x-1/x)^2=x^2+1/x^2-2=16

x^2+1/x^2=18

2.16[1/(x^2-10+1/x^2)]=16[1/(18-10)]=16/8=2

楼主第二道题抄错了吧

(1)已知x-1/x=4
x²+1/x²
=(x²-2+1/x²)+2
=(x-1/x)²+2
=16+2
=18
(2)16x²/(x^4-10x+1)
=16/(x²+1/x²-10/x)
=16/(18-10/x)
=8/(9-5/x)
题目是不是有点问题?!应为10x²
16x²/(x^4-10 x²+1)
=16/(x²+1/x²-10)
=16/(18-10)
=2