a: \(=\left(x+z\right)^2-\left(y-t\right)^2=\left(x+z+y-t\right)\left(x+z-y+t\right)\)
c: \(=x^2y+xy^2+y^2z+yz^2+x^2z+xz^2+2xyz\)
\(=x^2y+x^2z+xy^2+2xyz+xz^2+y^2z+yz^2\)
\(=x^2\left(y+z\right)+x\left(y+z\right)^2+yz\left(y+z\right)\)
\(=\left(y+z\right)\left(x^2+xy+xz+yz\right)\)
\(=\left(y+z\right)\left(x+y\right)\left(x+z\right)\)