1. The problem is to understand the interval $[-1,3]$ and what it represents. 2. The interval $[-1,3]$ is a set of all real numbers $x$ such that $-1 \leq x \leq 3$. 3. This means the interval includes all numbers starting from $-1$ up to $3$, including the endpoints $-1$ and $3$. 4. Intervals are often used to describe domains or ranges of functions, or to specify where a variable can lie. 5. In this case, the square brackets $[\ ]$ indicate that the endpoints are included (closed interval). 6. If the interval were $(-1,3)$ with parentheses, it would mean the endpoints are not included (open interval). 7. So, $[-1,3]$ means $x$ can be $-1$, $3$, or any number in between. 8. This is a fundamental concept in algebra and calculus when dealing with domains, ranges, or integration limits.