Đáp án:
$\displaystyle \begin{array}{{>{\displaystyle}l}} a.\ 2x^{3} y+2x^{2} y^{2} -6xy^{3}\\ b.\ 3x^{3} +2x^{2} +8x\\ c.\ x^{2} +x-10\\ d.\ 4y^{2} \end{array}$
Giải thích các bước giải:
$\displaystyle \begin{array}{{>{\displaystyle}l}} a.\ 2xy\left( x^{2} +xy-3y^{2}\right) =2x^{3} y+2x^{2} y^{2} -6xy^{3}\\ b.\ ( x+2)\left( 3x^{2} -4x\right) =3x^{3} +6x^{2} -4x^{2} +8x=3x^{3} +2x^{2} +8x\\ c.\ \left( x^{3} +3x^{2} -8x-20\right) :( x+2)\\ =\frac{x^{3} +2x^{2} +x^{2} +2x-10x-20}{x+2}\\ =\frac{x^{2}( x+2) +x( x+2) -10( x+2)}{x+2}\\ =\frac{\left( x^{2} +x-10\right)( x+2)}{( x+2)} =x^{2} +x-10\\ d.\ ( x+y)^{2} +( x-y)^{2} -2( x+y)( x-y)\\ =(( x+y-( x-y))^{2} =( 2y)^{2} =4y^{2} \end{array}$
