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