Lesson objective: Determine missing angles using the triangle angle sum.

This lesson helps to build procedural skill with triangle sum of triangles. Visual representations are used here to support students as they determine angle relationships that help them find missing angle measures. This work develops students' understanding that equations can be used to represent the interior angle sums of a triangle always equal 180º.

Students engage in Mathematical Practice #7 as they use the structure of parallel lines, angles, and triangles from earlier experiences to assist them. As students engage in productive struggle, they identify efficient ways to approach these types of geometric multi-step problems.

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