2x ²chia 1+x ² =y, 2y ² chia 1+y ²=z, 2z ²chia cho 1+z ² =x

`a)` 

$\dfrac{2x^2}{1 + x^2 }$ `=` `y`
`⇒` `x = 1 ` `;` `y = 1`
`⇒` $\dfrac{2 . 1^2}{1 + 1^2}$ `=` `1`
`⇒` `2/2` `=` `1`
`b)` 
$\dfrac{2y^2}{1 + y^2 }$ `=` `z`
`⇒` `y = 1` `;` `z = 1`
`⇒` $\dfrac{2 . 1^2}{1 + 1^2 }$ `=` `1`
`⇒` `2/2` `=` `1`
`c)`
$\dfrac{2z^2}{1 + z^2 }$ `=` `x`
`⇒` `z = 1` `;` `x = 1`
`⇒` $\dfrac{2 . 1^2}{1 + 1^2 }$ `=` `1`
`⇒` `2/2` `=` `1`
$\text{Chúc bạn học tốt ^^ }$