a, \(\left(x^2+2x+3\right)\left(x+2\right)=x^3+2x^2+3x+2x^2+4x+6=x^3+4x^2+7x+6\)
b, \(\left(x^2+xy+y^2\right)\left(x-y\right)=x^3-y^3\)
c, \(\left(x+y\right)\left(x^2-xy+y^2\right)=x^3+y^3\)
a: Ta có: \(\left(x^2+2x+3\right)\left(x+2\right)\)
\(=x^3+2x^2+2x^2+4x+3x+6\)
\(=x^3+4x^2+7x+6\)
b: Ta có: \(\left(x-y\right)\left(x^2+xy+y^2\right)\)
\(=x^3+x^2y+xy^2-x^2y-xy^2-y^3\)
\(=x^3-y^3\)
c: Ta có: \(\left(x+y\right)\left(x^2-xy+y^2\right)\)
\(=x^3-x^2y+xy^2+x^2y-xy^2+y^3\)
\(=x^3+y^3\)