f is decreasing on the intervals (-∞, 1/3) and (3, ∞).
f is negative on the intervals (-1, 2) and (4, ∞).
f is increasing on the intervals (1/3, 3).
f is positive on the intervals (-∞, -1) and (2, 4).
For any given function, y = f(x), if the output value is decreasing when the input value is increased, then, the function is generally referred to as a decreasing function;
The polynomial function, f is decreasing on the intervals (-∞, 1/3) and (3, ∞).
For any given function, y = f(x), if the output value is increasing when the input value (domain) is increased, then, the function is generally referred to as an increasing function.
The polynomial function, f is increasing on the intervals (1/3, 3) only.
A function is positive when the output value is greater than zero i.e [f(x) > 0]. Conversely, a function is negative when the output value is less than zero i.e [f(x) < 0].