Domian & Ranges

cube root function f(x) = 3 √ x (Square root of x cubed) Domain: (−∞, ∞) Range: (−∞, ∞)

The domain and range include all real numbers. Note that there is no problem taking a cube root, or any odd-integer root, of a negative number, and the resulting output is negative (it is an odd function).

constant function f(x) = c Domain: (−∞, ∞) Range: [c, c]

The domain consists of all real numbers; there are no restrictions on the input. The only output value is the constant c, so the range is the set {c} that contains this single element. In interval notation, this is written as [c, c], the interval that both begins and ends with c.

cubic function f(x) = x 3 Domain: (−∞, ∞) Range: (−∞, ∞)

The domain is all real numbers because the horizontal extent of the graph is the whole real number line. The same applies to the vertical extent of the graph, so the domain and range include all real numbers.

identity function f(x) = x Domain: (−∞, ∞) Range: (−∞, ∞)

There is no restriction on x. Both the domain and range are the set of all real numbers.

absolute value function f(x) = ∣ x ∣ Domain: (−∞, ∞) Range: [0, ∞)

There is no restriction on x. However, because absolute value is defined as a distance from 0, the output can only be greater than or equal to 0.

reciprocal function f(x) = 1/x Domain: (−∞, 0) ∪ (0, ∞) Range: (−∞, 0) ∪ (0, ∞)

We cannot divide by 0, so we must exclude 0 from the domain. Further, 1 divided by any value can never be 0, so the range also will not include 0. In set-builder notation, we could also write {x | x ≠ 0}, the set of all real numbers that are not zero.

reciprocal squared function f(x) = 1/x squared) Domain: (−∞, 0) ∪ (0, ∞) Range: (0, ∞)

We cannot divide by 0, so we must exclude 0 from the domain. There is also no x that can give an output of 0, so 0 is excluded from the range as well. Note that the output of this function is always positive due to the square in the denominator, so the range includes only positive numbers.

square root function f(x) = √x (square root of x) Domain: [0, ∞) Range: [0, ∞)

We cannot take the square root of a negative real number, so the domain must be 0 or greater. The range also excludes negative numbers because the square root of a positive number x is defined to be positive, even though the square of the negative number −√ x also gives us x.

quadratic function f(x) = x 2 Domain: (−∞, ∞) Range: [0, ∞)

the domain is all real numbers since the horizontal extent of the graph is the whole real number line. Because the graph does not include any negative values for the range, the range is only non-negative real numbers.