a: =x(x+3)-4(x+3)=(x+3)(x-4)
b: \(=\left(2x-1\right)^2-y^2=\left(2x-1-y\right)\left(2x-1+y\right)\)
c: \(=\left(a-1\right)^2-b^2=\left(a-1-b\right)\left(a-1+b\right)\)
d: \(=y^2\left(x+y\right)-z\left(x+y\right)=\left(x+y\right)\left(y^2-z\right)\)
d: \(=y\left(16x^3+\dfrac{1}{4}z\right)\)