\(xyz-\left(xy+yz+xz\right)+\left(x+y+z\right)-1\)

\(=xyz-xy-yz+y-xz+x+z-1\)

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

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

\(=[\left(x-1\right)y-\left(x-1\right)]\left(z-1\right)\)

\(=\left(x-1\right)\left(y-1\right)\left(z-1\right)\)

       \(xyz-\left(xy+yz+xz\right)+\left(x+y+z\right)-1\)

\(=\left(xyz-xy-xz+x\right)-yz+y+z-1\)

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

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

\(=\left(x-1\right)\left[y\left(z-1\right)-\left(z-1\right)\right]\)

\(=\left(x-1\right)\left(y-1\right)\left(z-1\right)\)

\(a,=\left(xy-1-x-y\right)\left(xy-1+x+y\right)\\ b,Sửa:a^3+2a^2+2a+1\\ =a^3+a^2+a^2+a+a+1=\left(a+1\right)\left(a^2+a+1\right)\\ c,=1-4a^2-a\left(a^2-4\right)=1-4a^2-a^3+4a\\ =\left(1-a\right)\left(1+a+a^2\right)+4a\left(1-a\right)\\ =\left(1-a\right)\left(1+5a+a^2\right)\\ d,=\left(a^2-a^2b^2\right)+\left(b^2-b\right)+\left(ab-a\right)\\ =a^2\left(1-b\right)\left(1+b\right)+b\left(b-1\right)+a\left(b-1\right)\\ =\left(b-1\right)\left(-a^2-ab+b+a\right)\\ =\left(b-1\right)\left(b-1\right)\left(a+b\right)\left(1-a\right)\)

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

\(f,=xyz-xy-yz-xz+x+y+z-1\\ =xy\left(z-1\right)-y\left(z-1\right)-x\left(z-1\right)+\left(x-1\right)\\ =\left(z-1\right)\left(xy-y-x+1\right)=\left(z-1\right)\left(x-1\right)\left(y-1\right)\)

b) Ta có: \(x^3-x^2y-xy^2+y^3\)

\(=\left(x^3+y^3\right)-\left(x^2y+xy^2\right)\)

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

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

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

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)

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

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

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

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

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

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

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

     xy( x+ y) + yz(y+z) + xz(x+z) + 3xyz

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

= zy(x+y+z) + yz(x + y + z) + xz ( x+y+z)

 = ( x+ y +z )( xy + yz + zx) 

xy(x+y)+yz(y+z)+xz(x+z)+2xyz 

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

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

= xy(x + y) + z(x + y + z)(y + x) 

= (x + y)(xy + zx + zy + z²) 

= (x + y)[x(y + z) + z(y + z)] 

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