Learning Objectives

State the domain and variety of a relation. Determine a function. Use duty notation.

Graphs, Relations, Domain, and Range

The rectangular coordinate systemA system with 2 number present at appropriate angles specifying points in a airplane using ordered pairs (x, y). Consists of two genuine number currently that crossing at a right angle. The horizontal number heat is dubbed the x-axisThe horizontal number line provided as reference in a rectangle-shaped coordinate system., and also the upright number heat is referred to as the y-axisThe upright number line offered as reference in a rectangular coordinate system.. These 2 number lines define a flat surface dubbed a planeThe flat surface defined by x- and also y-axes., and also each suggest on this plane is associated with an notified pairPairs (x, y) that identify position loved one to the beginning on a rectangular coordinate plane. Of actual numbers (x, y). The first number is called the x-coordinate, and also the 2nd number is referred to as the y-coordinate. The intersection of the 2 axes is known as the originThe point where the x- and y-axes cross, denoted through (0, 0)., which corresponds to the allude (0, 0).

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The x- and also y-axes break the plane into four regions dubbed quadrantsThe four regions the a rectangle-shaped coordinate airplane partly bounded by the x- and y-axes and numbered using the roman numerals I, II, III, and IV., called using roman inn numerals I, II, III, and also IV, together pictured. The ordered pair (x, y) represents the position of points family member to the origin. Because that example, the ordered pair (−4, 3) represents the position 4 systems to the left that the origin, and 3 units above in the second quadrant.


This device is often called the Cartesian name: coordinates systemTerm used in honor of René Descartes when referring come the rectangle-shaped coordinate system., called after the French mathematician René Descartes (1596–1650).

Figure 2.1


Rene Descartes Wikipedia

Next, we specify a relationAny set of ordered pairs. As any set of notified pairs. In the paper definition of algebra, the connections of interest are sets that ordered pairs (x, y) in the rectangular coordinate plane. Typically, the works with are associated by a dominion expressed making use of an algebraic equation. Because that example, both the algebraic equations y=|x|−2 and also x=|y|+1 specify relationsips in between x and y. Following are some integers that satisfy both equations:


Here two relations consisting of seven ordered pair solutions are obtained:

y=|x|−2   has solutions   (−3,1),(−2,0),(−1,−1),(0,−2),(1,−1),(2,0),(3,1)andx=|y|+1   has solutions   (4,−3),(3,−2),(2,−1),(1,0),(2,1),(3,2),(4,3)

We deserve to visually display any kind of relation that this form on a coordinate aircraft by plotting the points.


The solution sets of each equation will type a relationship consisting that infinitely many ordered pairs. We deserve to use the provided ordered pair services to estimate every one of the various other ordered bag by illustration a line through the given points. Here we put an arrow on the end of our lines to indicate that this collection of notified pairs continues without bounds.


The representation of a relation on a rectangle-shaped coordinate plane, as shown above, is called a graphA visual depiction of a relationship on a rectangular coordinate plane.. Any type of curve graphed ~ above a rectangle-shaped coordinate aircraft represents a set of ordered pairs and thus specifies a relation.

The collection consisting of all of the first components of a relation, in this instance the x-values, is dubbed the domainThe collection consisting of all of the an initial components the a relation. For connections consisting of points in the plane, the domain is the collection of every x-values.. And the set consisting of all 2nd components the a relation, in this instance the y-values, is referred to as the rangeThe collection consisting of all of the 2nd components that a relation. For relationships consisting of point out in the plane, the variety is the set of every y-values. (or codomainUsed when referencing the range.). Often, we have the right to determine the domain and range of a relationship if us are provided its graph.

Here we can see that the graph that y=|x|−2 has a domain consisting of all real numbers, ℝ=(−∞,∞), and also a variety of all y-values higher than or same to −2, <−2,∞). The domain the the graph of x=|y|+1 is composed of every x-values better than or same to 1, <1,∞), and the variety consists the all actual numbers, ℝ=(−∞,∞).


The minimum x-value stood for on the graph is −8 all others room larger. Therefore, the domain is composed of all x-values in the interval <−8,∞). The minimum y-value represented on the graph is 0; thus, the selection is <0,∞).


Of unique interest are relations where every x-value synchronizes to precisely one y-value. A relation through this residential or commercial property is referred to as a functionA relation wherein each element in the domain corresponds to exactly one facet in the range..

Example 2

Determine the domain and variety of the following relation and state whether it is a role or not: (−1, 4), (0, 7), (2, 3), (3, 3), (4, −2)


Here we different the domain (x-values), and also the variety (y-values), and depict the correspondence between the values through arrows.

The relation is a duty because every x-value coincides to exactly one y-value.

Answer: The domain is −1, 0, 2, 3, 4 and also the variety is −2, 3, 4, 7. The relation is a function.

Example 3

Determine the domain and range of the complying with relation and state whether it is a role or not: (−4, −3), (−2, 6), (0, 3), (3, 5), (3, 7)


The provided relation is not a function because the x-value 3 coincides to two y-values. Us can also recognize attributes as connections where no x-values room repeated.

Answer: The domain is −4, −2, 0, 3 and the range is −3, 3, 5, 6, 7. This relation is no a function.

Consider the relations consisting of the 7 ordered pair solutions to y=|x|−2 and x=|y|+1. The correspondence between the domain and range of each deserve to be pictured together follows:

Notice that every aspect in the domain of the solution collection of y=|x|−2 synchronizes to just one aspect in the range; the is a function. The options to x=|y|+1, ~ above the other hand, have values in the domain that correspond come two elements in the range. In particular, the x-value 4 corresponds to 2 y-values −3 and also 3. Therefore, x=|y|+1 does not specify a function.

We can visually identify attributes by their graphs making use of the vertical heat testIf any type of vertical line intersects the graph much more than once, then the graph walk not stand for a function.. If any kind of vertical heat intersects the graph much more than once, climate the graph walk not stand for a function.

The vertical heat represents a worth in the domain, and also the number of intersections with the graph represent the number of values to which it corresponds. As we deserve to see, any vertical line will certainly intersect the graph of y=|x|−2 just once; therefore, it is a function. A upright line have the right to cross the graph of x=|y|+1 more than once; therefore, the is no a function. Together pictured, the x-value 3 coincides to an ext than one y-value.

Example 4

Given the graph, state the domain and variety and identify whether or not it represents a function:


From the graph we can see that the minimum x-value is −1 and also the maximum x-value is 5. Hence, the domain consists of all the genuine numbers in the set from <−1,5>. The preferably y-value is 3 and the minimum is −3; hence, the selection consists that y-values in the expression <−3,3>.

In addition, because we can find a vertical line that intersects the graph an ext than once, we conclude the the graph is not a function. There are countless x-values in the domain that correspond to two y-values.

Answer: Domain: <−1,5>; range: <−3,3>; function: no

Try this! provided the graph, recognize the domain and selection and state even if it is or no it is a function:

Function Notation

With the an interpretation of a function comes unique notation. If we think about each x-value to it is in the input the produces precisely one output, climate we deserve to use duty notationThe notation f(x)=y, i beg your pardon reads “f the x is equal to y.” provided a function, y and also f(x) can be supplied interchangeably.:


The notation f(x) reads, “f the x” and also should not be puzzled with multiplication. Algebra frequently involves functions, and so the notation becomes useful when performing typical tasks. Right here f is the duty name, and also f(x) denotes the worth in the variety associated through the worth x in the domain. Features are often named with various letters; some typical names for attributes are f, g, h, C, and R. We have established that the collection of options to y=|x|−2 is a function; therefore, using role notation we deserve to write:


It is necessary to note that y and also f(x) are supplied interchangeably. This notation is provided as follows:

 f(x)   =  | x |−2↓ ↓f(−5)=|−5|−2=5−2=3

Here the compact notation f(−5)=3 shows that whereby x=−5 (the input), the role results in y=3 (the output). In other words, change the variable v the value offered inside the parentheses.

Functions are compactly identified by an algebraic equation, such together f(x)=|x|−2. Given values for x in the domain, us can easily calculate the corresponding values in the range. Together we have seen, features are additionally expressed utilizing graphs. In this case, we analyze f(−5)=3 as follows:

Function notation streamlines the job of evaluating. For example, usage the function h identified by h(x)=12x−3 to evaluate because that x-values in the collection −2, 0, 7.

h(−2)=12(−2)−3=−1−3=−4 h(0)=12(0)−3=0−3=−3h(7)=12(7)−3=72−3=12

Given any duty defined by h(x)=y, the value x is called the dispute of the functionThe worth or algebraic expression provided as input once using duty notation.. The discussion can be any kind of algebraic expression. Because that example:


Example 5

Given g(x)=x2, uncover g(−2), g(12), and also g(x+h).


Recall that as soon as evaluating, it is a ideal practice to begin by replacing the variables with parentheses and also then instead of the suitable values. This helps v the bespeak of operations when simplifying expressions.


Answer: g(−2)=4, g(12)=14, g(x+h)=x2+2xh+h2

At this point, the is important to note that, in general, f(x+h)≠f(x)+f(h). The vault example, whereby g(x)=x2, illustrates this nicely.


Example 6

Given f(x)=2x+4, uncover f(−2), f(0), and also  f(12a2−2).



Answer: f(−2)=0, f(0)=2,  f(12a2−2)=|a|

Example 8

Given f(x)=5x+7, uncover x whereby f(x)=27.


In this example, the calculation is given and also we are asked to find the input. Substitute f(x) with 27 and solve.


Therefore, f(4)=27. As a check, we have the right to evaluate f(4)=5(4)+7=27.

Answer: x=4


Here we space asked to discover the x-value provided a particular y-value. We start with 2 on the y-axis and also then check out the matching x-value.

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Key Takeaways

A relationship is any collection of notified pairs. However, in this course, we will be working v sets the ordered bag (x, y) in the rectangular coordinate system. The collection of x-values specifies the domain and the set of y-values specifies the range. Special relationships where every x-value (input) synchronizes to precisely one y-value (output) are referred to as functions. We can quickly determine whether or not an equation represents a role by performing the vertical line test top top its graph. If any vertical line intersects the graph more than once, climate the graph walk not represent a function. If one algebraic equation defines a function, climate we can use the notation f(x)=y. The notation f(x) is review “f that x” and also should no be puzzled with multiplication. Once working v functions, it is crucial to remember the y and also f(x) are provided interchangeably. If request to discover f(a), we substitute the discussion a in because that the variable and also then simplify. The argument could be an algebraic expression. If request to uncover x where f(x)=a, we set the duty equal to a and then settle for x.

Topic Exercises

Part A: Relations and Functions

Determine the domain and selection and state even if it is the relationship is a function or not.