Giải cho tôi câu hỏi

`(x^2 -2yz + z^2) + (3yz  - z^2 + 5x^2)`

`= x^2 -2yz + z^2 + 3yz  - z^2 + 5x^2`

`= (x^2 + 5x^2) + ( -2yz + 3yz) +(z^2 - z^2)`

`= 6x^2 + yz`

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`(x^2 - 2xy + y^2) + (y^2 + 2xy + x^2 + 1)`

`=x^2 - 2xy + y^2 + y^2 + 2xy + x^2 + 1`

`=(x^2 + x^2) + (-2xy + 2xy) + (y^2 + y^2) + 1 `

`= 2x^2 + 2y^2 +1`