\(x^2y+y^2x+x^2z+z^2x+y^2z+z^2y+2xyz\)..

\(=\left(x^2y+z^2y+2xyz\right)+\left(y^2x+y^2z\right)+\left(z^2x+x^2z\right)\).

\(=y\left(x+z\right)^2+y^2\left(x+z\right)+xz\left(x+z\right)\)

\(=\left(xy+yz\right)\left(x+z\right)+\left(x+z\right)\left(y^2+xz\right)\).

\(=\left(x+z\right)\left(xy+yz+y^2+xz\right)\).

\(=\left(x+z\right)\left[x\left(y+z\right)+y\left(y+z\right)\right]\).

\(=\left(x+z\right)\left(x+y\right)\left(y+z\right)\).

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

xy(x + y) + yz(y + z) + xz(x + z) + 2xyz

= x 2 y + x y 2  + yz(y + z) +  x 2 z + x z 2  + xyz + xyz

= ( x 2 y +  x 2 z) + yz(y + z) + (x y 2  + xyz) + (x z 2  + xyz)

=  x 2 (y + z) + yz(y + z) + xy(y+ z) + xz(y + z)

= (y + z)(  x 2  + yz + xy + xz) = (y + z)[( x 2  + xy) + (xz + yz)]

= (y + z)[x(x + y) + z(x + y)] = (y + z)(x+ y)(x + z)

1 ) \(x^2-x-y^2-y=\left(x^2-y^2\right)+\left(-x-y\right)=\left(x+y\right)\left(x-y\right)-\left(x+y\right)=\left(x+y\right)\left(x-y-1\right)\)

2 ) \(x^2-2xy+y^2-z^2=\left(x-y\right)^2-z^2=\left(x-y+z\right)\left(x-y-z\right)\)

3 ) \(5x-5y+ax-ay=5.\left(x-y\right)+a\left(x-y\right)=\left(x-y\right)\left(5+a\right)\)

4 ) \(a^3-a^2x-ay+xy=a^2.\left(a-x\right)-y.\left(a-x\right)=\left(a-x\right)\left(a^2-y\right)\)

5 ) \(xy.\left(x+y\right)+yz.\left(y+z\right)+xz.\left(x+z\right)+2xyz\)

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

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

\(=xy.\left(x+y\right)+yz.\left(x+y\right)+z^2.\left(x+y\right)+xz.\left(x+y\right)\)

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

\(=\left(x+y\right)\left[x.\left(y+z\right)+z.\left(y+z\right)\right]=\left(x+y\right)\left(y+z\right)\left(x+z\right)\)

x^2-2xy+y^2-z^2

= (x-y)^2 - z^2

= (x-y-z)(x-y+z)

5x-5y+5x-ay

xy(x+y)+yz(y+z)+xz(x+z)+2xyz

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

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

\(=xy\left(x+y+z\right)+xz\left(x+z+y\right)+yz\left(y+z\right)\)

\(=x\left(x+y+z\right)\left(y+z\right)+yz\left(y+z\right)\)

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

\(=\left(y+z\right)\left[x\left(x+z\right)+y\left(x+z\right)\right]\)

\(=\left(y+z\right)\left(x+z\right)\left(x+y\right)\)

b, \(2x^2+2y^2-x^2z+z-y^2z-2\)

\(=\left(2x^2-x^2z\right)+\left(2y^2-y^2z\right)-\left(2-z\right)\)

\(=x^2\left(2-z\right)+y^2\left(2-z\right)-\left(2-z\right)\)

\(=\left(2-z\right)\left(x^2+y^2-1\right)\)