## Calculus with Applications (10th Edition)

$x\leq-1$
The $''(-\infty,...''$indicates that this interval contains numbers that can be negative and unbounded in magnitude (so there is no left endpoint). At the same time, they are less or equal to $-1$, since the bracket on the right indicates that the right endpoint is included.. In less words, these are numbers that are less than or equal to $-1$. For a number x from this interval, we can write $x\leq-1$