Measuring Supplementary and Complementary Angles

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.