Curated OER
Angle Sum of Triangles and Quadrilaterals
In this angle sum instructional activity, students find missing angles of 20 triangles and quadrilaterals. Students find the missing angle in each polygon by using the total degrees of each and given angle measures.
CK-12 Foundation
Ck 12: Elem Math: Determining the Unknown Angle in a Triangle
[Free Registration/Login may be required to access all resource tools.] Students watch a video and attempt practice problems on how to determine a missing angle in a triangle.
Math Open Reference
Math Open Reference: Supplementary Angles
Learn about supplementary angles with this helpful reference tool. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.