$\text { Đáp án: }$
$\text { M + N }$
$\text { = 2x² – 2xy + 1 + 2y² + 2xy + 1 }$
$\text { = 2x² – 2xy + 2xy + 2y² + 1 + 1 }$
$\text { = 2x² + 2y² + 2 }$
$\text { M – N }$
$\text { = (2x² – 2xy + 1) – (2y² + 2xy + 1) }$
$\text { = 2x² – 2xy + 1 – 2y² – 2xy – 1 }$
$\text { = 2x² – 2xy – 2xy – 2y² + 1 – 1 }$
$\text { = 2x² – 4xy – 2y² }$