## Algebra: A Combined Approach (4th Edition)

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, to simplify $x^{2}\times x^{7}$, keep the base and add the exponents. $x^{2}\times x^{7}=x^{2+7}=x^{9}$