\(a)\)\(\left(x^2-5\right)\left(x+3\right)\)
\(b)\left(x+4\right)\left(x-x^2\right)\)
\(c)\left(x^2-6\right)\left(x+2\right)+\left(x+3\right)\left(x-x^2\right)\)
\(d)x\left(x-y\right)-y\left(x-y\right)\)
\(e)x^2\left(x+y\right)-x\left(x^2-y\right)\)
\(f)3x\left(12x-4\right)-9x\left(4x-3\right) \)