1. The problem asks us to determine the interval(s) where the function $f(x) = -4$ is negative. 2. The function $f(x) = -4$ is a constant function, meaning it has the same value for all $x$ in its domain. 3. Since $f(x) = -4$ for every $x$, and $-4$ is less than 0, the function is negative for all real numbers. 4. Therefore, the function is negative on the entire real line, which is the interval $]-\infty, \infty[$. 5. Among the given options, this corresponds to option (c) $]-\infty, \infty[$. Final answer: The function $f(x) = -4$ is negative on the interval $]-\infty, \infty[$.