How to Find Domain and Range of Relation

Step-by-Step Guide to Find Domain and Range of a Relation

Here is a step-by-step guide to finding the domain and range of a relation:

Step 1: Distinguish the Relation Type

• Determine whether your relation is described by a table, a graph, an equation, or a written description. The method for finding the domain and range may vary based on this.

Step 2: For Tabulated Relations (Ordered Pairs)

• Domain: List out all the unique \(x\)-values.
• Range: List out all the unique \(y\)-values.

Step 3: For Graphical Representations

• Domain: Identify the leftmost and rightmost points of the graph. This gives the range of \(x\)-values the relation spans.
• Range: Identify the highest and lowest points of the graph to determine the \(y\)-values the relation encompasses.

Step 4: For Equations

• Rational Functions: For fractions, the denominator should never be zero. Solve for values of \(x\) that would make the denominator zero and exclude them from the domain.
• Radical Functions: For even roots, the radicand (value inside the root) should be non-negative. Determine the \(x\)-values for which the radicand is non-negative.
• Logarithmic Functions: The argument of the log must be greater than zero.
• Domain: Solve for \(x\)-values taking into account the restrictions from the above function types.
• Range: Depending on the function type, deducing the range might be straightforward or require deeper analysis.

Step 5: Consider Restrictions

• Mathematical restrictions (like those mentioned in the equations section).
• Physical or real-world constraints (e.g., a relation describing time and growth might have a domain limited to positive values).

Step 6: State the Domain and Range in Proper Notation

• Interval Notation: Uses brackets and parentheses to describe intervals of values. For example, \([a,b]\) denotes all values between a and b, inclusive.
• Set-builder Notation: Defines a set by specifying its properties. For instance, {\(x∣x>2\)} represents all \(x\)-values greater than \(2\).

Step 7: Examine for Implicit Restrictions

• Sometimes, the domain and range might be restricted by the context or the nature of the relation, even if not explicitly mentioned.

Step 8: Cross-verify Using Multiple Methods:

• Whenever possible, approach the problem using different techniques. For instance, if you’ve derived the domain from an equation, try sketching a graph to visually verify the domain.

Step 9: Complex Relations and Composite Functions

• For relations involving multiple functions or operations (like the composition of functions), determine the domain and range of each part individually before combining them.

Step 10: Iterative Reflection and Refinement

• Reevaluate your conclusions. Sometimes, upon deeper reflection or by considering another perspective, you might spot oversights or nuances you missed in your initial analysis.

By meticulously following these steps and maintaining a comprehensive approach, the intricate task of determining the domain and range of a relation, even one of high complexity, can be systematically and effectively tackled.

Examples:

Example 1:

Consider the relation \(S=\){\((4,6),(5,7),(6,8),(7,6)\)}.

Determine the domain and range of the relation.

Solution:

To determine the domain, list all the \(x\)-values from the ordered pairs: \(4,5,6,7\)

So, the domain of relation \(S\) is {\(4, 5, 6, 7\)}.

Next, to determine the range, list all the \(y\)-values from the ordered pairs: \(6,7,8,6\)

After removing the duplicates, the range of relation \(S\) is {\(6,7,8\)}.

Example 2:

Consider the relation \(T=\){\((−2,0),(0,−1),(2,1),(3,0)\)}.

Determine the domain and range of the relation.

Solution:

To determine the domain, list all the \(x\)-values from the ordered pairs: \(−2,0,2,3\)

So, the domain of relation \(T\) is {\(-2, 0, 2, 3\)}.

Next, to determine the range, list all the \(y\)-values from the ordered pairs: \(0,−1,1,0\)

After removing the duplicates, the range of relation \(T\) is {\(-1, 0, 1\)}.