$$\frac{2}{3}x^{2}+\frac{2}{3}(x-2)(x+2)n^{2}.$$
$\frac{2\left(n^{2}\left(x^{2}-4\right)+x^{2}\right)}{3}$
$\frac{2x^{2}+2\left(nx\right)^{2}-8n^{2}}{3}$
