Which could be the entire interval over witch the function, f(x) is negative?

Check the picture below.

so, plotting the first 5 points, let's notice f(x) is below the x-axis, and thus negative, after x = -4, going further to the left, it remains in the negative quadrants, down down down up to -∞.

notice, we use the parentheses for the -∞, because we don't know where it's, thus we'll never touch it, and we also use a parentheses on the -4, because, when x = -4, f(x) = 0, 0 is not a negative value, so -4) because  is not included in the interval, but all numbers before it are.

what is the original number? you forgot to add it.