In this lesson, you will learn how to determine the reasonableness of the domain and range of quadratic functions given a real world example.

How to Determine the Restricted Domain and Range of a Quadratic Function

If the domain and range of a quadratic function is not reasonable given a problem situation, then it may have restrictions. Use the process chart below as a guide for determining the restricted domain and range of a quadratic function given a real-world example. Click on each step to see an algorithm to check for restrictions.

Step 1
Read the problem and analyze the entire graph of the quadratic function. Close Pop Up
Step 2
Determine the domain and range of the function without restrictions. Close Pop Up
Step 3
Does this answer make sense for this specific problem situation? Why or why not? (Example: Given the problem situation, it does not make sense to have negative numbers within the domain.) Close Pop Up
Step 4
If the domain and range does not make sense, determine the domain and range with restrictions. Close Pop Up
Bird next with three eggs

A bird is building a nest in a tree 36 feet above the ground. The bird dropped a stick from the nest. The function f(x) = -16x2 + 36 describes the height of the stick in feet after x seconds. Identify the domain and range of the function.


Food for Thought

  1. What does the variable x represent in the function?

    Check Your Answer The variable x represents the number of seconds after the stick is dropped from the nest. Close Pop Up

  2. According to the graph, at what height did the bird drop the stick?

    Check Your Answer The bird drops the stick at 36 feet. Close Pop Up

  3. The points (-1, 20) and (2, -28) lie on the graph of the quadratic function f(x) = -16x2 + 36. What do these points mean?

    Check Your Answer The point (-1, 20) means at -1 second the stick is 20 feet above the ground. The point (2, -28) means at 2 seconds the stick is 28 feet below the ground. Close Pop Up


Click on each step to see the process in determining the restrictions for this problem.

Step 1

Read the problem and analyze the entire graph of the function f(x) = -16x2 + 36.

Graph of function f of x = -16x^2 + 36. Quadratic Functions, Rechneronline
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Step 2

Determine the domain and range of the function without restrictions. Use the answer box to drag and drop the correct answers into the correct location.

Interactive exercise. Assistance may be required.

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Step 3

Does your answer make sense for this specific problem? Why or why not?

Check Your Answer It does not make sense to include negative numbers within the domain because time cannot be negative. In addition, it does not make sense to include negative numbers within the range because the height of the stick does not extend below ground level. Close Pop Up Close Pop Up
Step 4

If the domain and range does not make sense, determine the domain and range with restrictions. Use the answer box to drag and drop the correct answers into the correct location.

Interactive exercise. Assistance may be required.

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Summary of the Bird Nest Problem
In summary, even though the graph of the function extends to other quadrants, the domain and range are restricted to quadrant 1 because negative numbers for time and height are not reasonable for this problem situation. Close Pop Up