Graphing Square Root Functions
A step by step tutorial on graphing and sketching square root functions . The graph, domain, range and sometimes the simplifications of these functions and other properties are discussed.
Review: The domain of function f defined by f(x) = √x is the set of all real positive numbers and zero because the square root of negative numbers are not real numbers (think of √ ( 4), is it real?). In inequality form, the domain of f(x) = √x is written as
in interval form the domain is given by
Example 1: Make a table of values of function f given below, graph it and find its range.
Solution to Example 1: Because the domain of f is the set of all positive real numbers and zero, we might construct a table of values as follows:
The values of x were selected so that the square root of these values are whole numbers which make it easy to plot the points shown in the table. The range of f is given by the interval [0 , +∞).
Example 2: Find the domain, make a table of values of function f given below, graph it and find its range.
Solution to Example 2: First find the domain of the square root function given above by stating that the expression under the square root must be positive or equal to zero x  3 ≥ 0 Solve the above inequality to obtain the domain of f as the set of all real values such that x ≥ 3 We now select values of x in the domain to construct a table of values.
Example 3: Find the domain, make a table of values of function f given below, graph it and find its range.
Solution to Example 3: The domain of the function given above is found by setting  2x + 4 ≥ 0 Solve the above inequality to obtain the domain of f as the set of all real values such that x ≤ 2 We now select values of x in the domain of f to construct a table of values. These values are selected so that the square root term is a whole number and give points that are easy to plot.
The range of f is given by the interval (∞ , 1].
Example 4: Find the domain of function f given below, graph it and find its range.
Solution to Example 4: The domain of function given above is found by solving the polynomial inequality  x^{ 2} + 4 ≥ 0 The solution set of the above inequality is given by the interval [2 , 2] which is also the domain of the above function. Let us write the given function as an equation as follows y = √ ( x^{ 2} + 4) Square both sides and arrange to obtain. x^{ 2} + y^{ 2} = 2^{ 2} The equation obtained is that of a circle. Hence the graph of f(x) = √ ( x^{ 2} + 4) is the upper half of a circle sinsce √ ( x^{ 2} + 4) is positive. Hence the graph below.
Example 5: Find the domain, make a table of values of function f given below, graph it and find its range.
Solution to Example 5: The domain of the function given above is found by solving x^{ 2}  9 ≥ 0 Which gives a domain reprsented by (∞ , 3] U [3 , + ∞) We now select values of x in the domain of f to construct a table of values, noting f(x) = f(x) hence a symmetry of the graph with respect to the y axis.
The range of f is given by the interval [0 , + ∞).
Example 6: Simplify f(x) given below, graph f and find its range.
Solution to Example 6: Let us use write the expression under the square root as a square as follows x^{ 2}  6x + 9 = (x  3)^{ 2} Hence f( x ) = √ (x^{ 2}  6x + 9) = √ ( (x  3)^{ 2} ) =  x  3  The given function has been rewitten as an absolute value function. Function f may be written as a piecewise function and graphed as follows. The range of f is given by the interval [0 , + ∞).
Example 7: Graph the radicand (expression under the radical sign), make a table of values of function f given below, graph f and find its range..
Solution to Example 7: Use completing the square to rewtite the expression under the square root as follows x^{ 2} + 4x + 6 = (x + 2)^{ 2} + 2 The expression under the square root is always positive hence the domain of f is the set of all real numbers. Let us first look at the graph of (x + 2)^{ 2} + 2. It is a parabola.
The range of f is given by the interval [√2 , + ∞). More references and links on graphing. Graphing Functions
