a) \(-\left(x+2\right)\cdot\left(x^2-1x+4\right)\)
\(=-\left(x+2\right)\cdot\left(x^2-x+4\right)\)
\(=-\left(x^3-x^2+4x+2x^2-2x+8\right)\)
\(=-\left(x^3+x^2+2x+8\right)\)
\(=-x^3-x^2-2x-8\)
b) \(-\left(x+2y\right)\cdot\left(x^2-2xy+y^2\right)\)
\(=-\left(x^3-2x^2y+xy^2+2x^2y-4xy^2+2y^3\right)\)
\(=-\left(x^3-3xy^2+2y^3\right)\)
\(=-x^3+3xy^2-2y^3\)
c) \(-\left(5-a\right)\cdot\left(25+5a+a^2\right)\)
\(=-\left(125-a^3\right)\)
\(=-125+a^3\)
d) \(-\left(x-2y\right)\cdot\left(x^2+2xy+4y^2\right)\)
\(=-\left(x^3-8y^3\right)\)
\(=-x^3+8y^3\)
a, sai đề
b, \(-\left(x+2y\right)\left(x^2-2xy+y^2\right)=-\left(x^3+y^3\right)\)
\(=-x^3-y^3\)
c, \(-\left(5-a\right)\left(25+5a+a^2\right)=-\left(125-a^3\right)\)
\(=a^3-125\)
d, \(-\left(x-2y\right)\left(x^2+2xy+4y^2\right)=-\left(x^3-8y^3\right)\)
\(=8y^3-x^3\)
