Rút gọn biểu thức: 

- Hướng dẫn giải

${\left(x-y+z\right)}^2$ + ${\left(z-y\right)}^2$ + 2(x – y + z)(y – z)

= ${\left(x-y+z\right)}^2$ + 2(x – y + z)(y – z) + ${\left(y-z\right)}^2$

= ${\left[\left(x-y+z\right)+\left(y-z\right)\right]}^2=x^2$