a) \(2x^3+6xy-x^2z-3yz\)
= \(\left(2x^3+6xy\right)-\left(x^2z+3yz\right)\)
=\(2x\left(x^2+3y\right)-z\left(x^2+3y\right)\)
=\(\left(x^2+2y\right)\left(2x-z\right)\)
b)\(x^2-6xy+9y^2-49\)
=\(x^2-2.x.3y+\left(3y\right)^2-7^2\)
=\(\left(x-3y\right)^2-7^2\)
=\(\left(x-3y+7\right)\left(x-3y-7\right)\)