<s>[INST] About $(x^3 - 4)^2 - x^6 + 2x^5 = 2x^5 -8x^3 + 16$ Studying polynomials I got the follows:
$$
    (x^3 - 4)^2 - x^6 + 2x^5 = 2x^5 -8x^3 + 16
$$
I can't understand from where we got this $-8x^3$.
I got to simplify this polynomial just to:
$$
2x^5 + 16
$$
Can someone help me understand from where we got the expression $-8x^3$ ?
 [/INST] $$\begin{align}
(x^3 - 4)^2 - x^6 + 2x^5 &= x^3\cdot x^3 + (-4)^2 + 2\cdot (-4) \cdot x^3 -x^6+ 2x^5\\
&=x^6-x^6 + 16 -8x^3 + 2x^5 = 2x^5 -8x^3 + 16
\end{align}
$$
</s>