Answer
$-16x^{7}$
Work Step by Step
Based on the product rule for exponents, we know that $a^{m}\times a^{n}=a^{m+n}$ (where $m$ and $n$ are positive integers and $a$ is a real number).
Therefore, $(2x^{3})(-8x^{4})=2\times-8\times x^{3+4}=-16x^{7}$.