Domain and Range of Relations from Graphs

A Complete Set of Examples and Detailed Practice Solutions

Understanding the domain (all possible $x$-values) and range (all possible $y$-values) of a relation from its graph is a critical algebraic skill. This page provides 10 comprehensive examples covering finite segments, infinite rays, and closed curves.

Quick Reference Guide

Section 1: Tutorial Examples

Example 1: Finite Line Segments

Identify the domain, range, and determine if the relation is a function:

Example 1 Graph
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Domain: $x$ ranges from point $A(-2, -4)$ to $B(4, -6)$:

\[ -2 \le x \le 4 \]

Range: The lowest point is $B(4, -6)$ and highest is $C(2, 2)$:

\[ -6 \le y \le 2 \]

Is it a function? Yes. No vertical line crosses the graph more than once.

Example 2: Diagonal Relation

Example 2 Graph
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Domain: Smallest $x$ at $A(-3, -5)$, largest at $B(8, 4)$:

\[ -3 \le x \le 8 \]

Range: Smallest $y$ at $A(-5)$, largest at $B(4)$:

\[ -5 \le y \le 4 \]

Is it a function? Yes, it passes the vertical line test.

Example 3: Non-Function Curve

Example 3 Graph
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Domain: From $A(-3, -2)$ to $B(1, -2)$:

\[ -3 \le x \le 1 \]

Range: Lowest point $C(-1, -5)$ to highest point $D(-1, 1)$:

\[ -5 \le y \le 1 \]

Is it a function? No. A vertical line crosses the graph at multiple points.

Vertical line check

Example 4: Infinite Ray (Closed)

Example 4 Graph
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Domain: Leftmost point is $A(-3, 0)$. The arrow points infinitely to the right:

\[ x \ge -3 \]

Range: Lowest points are $B, C$ at $y = -2$. The arrow points up:

\[ y \ge -2 \]

Is it a function? Yes.

Example 5: Infinite Ray (Open Circle)

Example 5 Graph
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Domain: Leftmost is $A(-2, -3)$ with an open circle. Graph extends right:

\[ x > -2 \]

Range: Lowest is $y = -3$ (excluded). Graph extends up:

\[ y > -3 \]

Is it a function? Yes.


Section 2: Practice Problems with Solutions

Question 6 (Practice 1)

Practice Question 1
View Solution

Domain: From $A(-8, -0.5)$ to $B(4, 0)$:

\[ -8 \le x \le 4 \]

Range: Lowest point $C(-3, -5)$ to highest $B(4, 0)$:

\[ -5 \le y \le 0 \]

Function: Yes.

Question 7 (Practice 2)

Practice Question 2
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Domain: $A(-2, 4)$ to $B(4, 6)$:

\[ -2 \le x \le 4 \]

Range: Lowest $C(2, -2)$ to highest $B(4, 6)$:

\[ -2 \le y \le 6 \]

Function: Yes.

Question 8 (Practice 3)

Practice Question 3
View Solution

Domain: Extends infinitely left, ends at $A(4, 2)$:

\[ x \le 4 \]

Range: Lowest $y = -2$ (points B and C), extends infinitely up:

\[ y \ge -2 \]

Function: Yes.

Question 9 (Practice 4)

Practice Question 4
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Domain: From $A(-5, -1)$ to $B(1, -1)$:

\[ -5 \le x \le 1 \]

Range: Lowest $C(-2, -3)$ to highest $D(-2, 1)$:

\[ -3 \le y \le 1 \]

Function: No. This is a closed curve; vertical lines hit it twice.

Non-function check 2

Question 10 (Practice 5)

Practice Question 5
View Solution

Domain: Starts at $A(-3, 1.8)$ with an open circle, extends infinitely right:

\[ x > -3 \]

Range: Highest is $B(-2, 2)$, extends infinitely down:

\[ y \le 2 \]

Function: Yes.

Further Resources