\(=x\left(x-4\right)\left(x+4\right)-15x\left(x-4\right)\\ =x\left(x-4\right)\left(x-11\right)\)
\(x^2-16x-15x\left(x-4\right)\)
\(=x\left(x-4\right)\left(x+4\right)-15x\left(x-4\right)\)
\(=\left(x-4\right)\left(x^2+4x-15x\right)\)
\(=\left(x-4\right)\left(x^2-11x\right)=x\left(x-4\right)\left(x-11\right)\)
\(x^3-16x-15x\left(x-4\right)\)
\(=x\left(x-4\right)\left(x+4\right)-15x\left(x-4\right)\)
\(=\left(x-4\right)\left(x^2+4x-15x\right)\)
\(=x\left(x-4\right)\left(x-11\right)\)