`2x^2-4x+1=0`

`\Delta=(-4)^2-4*2*1=8>0`

`->` Phương trình có hai nghiệm pb

Theo vi-et ta có:
`x_1+x_2=-b/a=-(-4)/2=2`

`x_1x_2=c/a=1/2` 

Suy ra: `A=(x_1^2-1/x_2)(x_2^2-1/x_1)`

`=x_1^2(x_2^2-1/x_1)-1/x_2(x_2^2-1/x_1)`

`=x_1^2x_2^2-x_1-x_2+1/(x_1x_2)`

`=(x_1x_2)^2-(x_1+x_2)+1/(x_1x_2)`

`=(1/2)^2-2+1/(1/2)`

`=1/4-2+2`

`=1/4`

Vậy: `A=1/4`