c. \(\dfrac{1}{2}x\left(x^2-4\right)+4\left(x+2\right)\)
= \(\dfrac{1}{2}x\left(x-2\right)\left(x+2\right)+4\left(x+2\right)\)
= \(\left[\dfrac{1}{2}x\left(x-2\right)-1\right]\left(x+2\right)\)
= \(\left(\dfrac{1}{2}x^2-1-1\right)\left(x+2\right)\)
= \(\left(\dfrac{1}{2}x^2-2\right)\left(x+2\right)\)
