\(xy\left(x+y\right)+yz\left(y+z\right)+xz\left(x+z\right)+2xyz\)
\(=x^2y+xy^2+y^2z+yz^2+x^2z+xz^2+2xyz\)
\(=\left(x^2y+x^2z+xz^2+xyz\right)+\left(xy^2+y^2z+yz^2+xyz\right)\)
\(=x\left(xy+xz+z^2+yz\right)+y\left(xy+yz+z^2+xz\right)\)
\(=\left(x+y\right)\left(xy+yz+xz+z^2\right)\)
\(=\left(x+y\right)\left[y\left(x+z\right)+z\left(x+z\right)\right]\)
\(=\left(x+y\right)\left(y+z\right)\left(x+z\right)\)
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