Activity Overview
In this activity, students will measure angles that supplementary or complementary. They are already given the measurement of the large angle (90° or 180°), and they need to find the values of the smaller angle measures. Hopefully, some students will recognize that they really only need to measure one of the angles and then subtract from the whole - or maybe you will explicitly teach that to your students. Discuss efficiency, double-checking, and problem-solving with your students to help their minds prepare to face new challenges with the knowledge they already know.
Supplementary Angles
Two angles that make a straight line together are called supplementary angles. A line, or straight angle, measures 180 degrees.
Complementary Angles
Two angles that make a right angle together are called complementary angles. A right angle measures 90 degrees.
For some students, using a protractor is extremely difficult, so they may need additional practice, modified assignments, or, most likely, both. Another way to tackle angle measures as additive is to use equations, such as 36° + h = 124°, with or without drawings. With only diagrams of angles, students can figure out how to set up an equation on their own. Without drawings, students strictly use algebra to find the value of the unknown variable rather than using a protractor to find the angle measurements. Both skills in algebra and tool manipulation are important and neither should be neglected.
Template and Class Instructions
(These instructions are completely customizable. After clicking "Copy Activity", update the instructions on the Edit Tab of the assignment.)
Student Instructions
Determine whether an angle is complementary or supplementary and measure the angles.
- Click "Start Assignment".
- Search "Math" or "Protractor" in the search bar and drag down the transparent protractor object.
- Measure each angle and record the measurements in the description box.
Lesson Plan Reference
Activity Overview
In this activity, students will measure angles that supplementary or complementary. They are already given the measurement of the large angle (90° or 180°), and they need to find the values of the smaller angle measures. Hopefully, some students will recognize that they really only need to measure one of the angles and then subtract from the whole - or maybe you will explicitly teach that to your students. Discuss efficiency, double-checking, and problem-solving with your students to help their minds prepare to face new challenges with the knowledge they already know.
Supplementary Angles
Two angles that make a straight line together are called supplementary angles. A line, or straight angle, measures 180 degrees.
Complementary Angles
Two angles that make a right angle together are called complementary angles. A right angle measures 90 degrees.
For some students, using a protractor is extremely difficult, so they may need additional practice, modified assignments, or, most likely, both. Another way to tackle angle measures as additive is to use equations, such as 36° + h = 124°, with or without drawings. With only diagrams of angles, students can figure out how to set up an equation on their own. Without drawings, students strictly use algebra to find the value of the unknown variable rather than using a protractor to find the angle measurements. Both skills in algebra and tool manipulation are important and neither should be neglected.
Template and Class Instructions
(These instructions are completely customizable. After clicking "Copy Activity", update the instructions on the Edit Tab of the assignment.)
Student Instructions
Determine whether an angle is complementary or supplementary and measure the angles.
- Click "Start Assignment".
- Search "Math" or "Protractor" in the search bar and drag down the transparent protractor object.
- Measure each angle and record the measurements in the description box.
Lesson Plan Reference
How Tos about Measuring Supplementary and Complementary Angles
Organize a hands-on angle scavenger hunt in your classroom
Engage students by challenging them to find and identify real-life examples of supplementary and complementary angles around the classroom. This activity helps reinforce angle concepts while making learning interactive and fun.
Explain the hunt rules and assign teams
Divide students into small groups or pairs and clearly explain that they will search for objects or corners forming right (90°) or straight (180°) angles. Providing structured groups boosts collaboration and ensures everyone participates.
Equip students with protractors and recording sheets
Hand out protractors and simple recording sheets so students can measure and document each angle they find. Using tools in real-world contexts builds confidence and accuracy in measurement skills.
Set a time limit and encourage creative thinking
Give students 10–15 minutes to search and record as many angles as they can. Encourage them to look in unexpected places, such as books, doors, whiteboards, or even chair legs. This keeps the activity fast-paced and exciting.
Review findings and discuss strategies as a class
Gather everyone to share their discoveries and talk about how they determined if each angle was complementary or supplementary. Highlight creative solutions and reinforce efficient measurement and reasoning strategies.
Frequently Asked Questions about Measuring Supplementary and Complementary Angles
What is the difference between supplementary and complementary angles?
Supplementary angles are two angles whose measures add up to 180 degrees (a straight line), while complementary angles add up to 90 degrees (a right angle).
How can students find a missing angle if they know the total is 90° or 180°?
Students can subtract the known angle from 90° (for complementary) or 180° (for supplementary) to find the missing angle. For example, if one angle is 36° in a complementary pair, the other is 90° – 36° = 54°.
What are some easy ways to teach students to measure angles using a protractor?
Start by showing how to align the protractor’s center with the angle’s vertex, and line up one side with the baseline. Have students read the correct scale and practice with clear diagrams and hands-on activities for better understanding.
Why do students struggle with using a protractor, and how can I help them?
Students may find protractors tricky due to alignment issues or reading the wrong scale. Help by providing step-by-step demonstrations, extra practice, and using transparent protractors for easier visualization.
Can students solve for unknown angle measures using equations instead of protractors?
Yes! Students can set up simple equations like angle + unknown = 90° or 180°. Solving the equation gives the missing angle, helping students practice both geometry and algebra skills.
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