Đáp án + Giải thích các bước giải:

   $(x + y + z)^5$- $x^5$- $y^5$- $x^5$

=  $x^{5}$ + $5x^{4}y$ + $5x^{4}z$ + $10x^{3}y^{2}$ + $20x^{3}yz$ + $10x^{3}z^{2}$ + $10x^{2}y^{3}$ + $30x^{2}y^{2}z$ + $30x^{2}yz^{2}$ + $10x^{2}z^{3}$ + $5xy^{4}$ + $20xy^{3}z$ + $30xy^{2}z^{2}$ + $20xyz^{3}$ + $5xz^{4}$ + $5y^{4}z$ + $10y^{3}z^{2}$ + $10y^{2}z^{3}$ + $5yz^{4}$ + $z^5$ + $y^{5}$ - $x^{5}$ - $y^{5}$ - $z^{5}$

= $5x^{4}y$ + $5x^{4}z$ + $10x^{3}y^{2}$ + $20x^{3}yz$ + $10x^{3}z^{2}$ + $10x^{2}y^{3}$ + $30x^{2}y^{2}z$ + $30x^{2}yz^{2}$ + $10x^{2}z^{3}$ + $5xy^{4}$ + $20xy^{3}z$ + $30xy^{2}z^{2}$ + $20xyz^{3}$ + $5xz^{4}$ + $5y^{4}z$ + $10y^{3}z^{2}$ + $10y^{2}z^{3}$ + $5yz^{4}$ + ($x^{5}$ - $x^{5}$) + ($y^{5}$ - $y^{5}$) + ($z^{5}$ - $z^{5}$) 

= $5x^{4}y$ + $5x^{4}z$ + $10x^{3}y^{2}$ + $20x^{3}yz$ + $10x^{3}z^{2}$ + $10x^{2}y^{3}$ + $30x^{2}y^{2}z$ + $30x^{2}yz^{2}$ + $10x^{2}z^{3}$ + $5xy^{4}$ + $20xy^{3}z$ + $30xy^{2}z^{2}$ + $20xyz^{3}$ + $5xz^{4}$ + $5y^{4}z$ + $10y^{3}z^{2}$ + $10y^{2}z^{3}$ + $5yz^{4}$ 

             $\color{pink}{\text{#anhcao31}}$