Question: User: i wrote
c\in)\-\infty,\-1)
1. The problem is to understand the notation $c \in (-\infty, -1)$.
2. This notation means that the variable $c$ belongs to the interval from negative infinity to $-1$, not including $-1$.
3. In interval notation, parentheses $()$ indicate that the endpoint is not included, so $c$ can be any number less than $-1$ but not equal to $-1$.
4. This is a way to express that $c$ is less than $-1$.
5. So, the solution set for $c$ is all real numbers $c$ such that $c < -1$.
Final answer: $c \in (-\infty, -1)$ means $c < -1$.