U1L19 Evidence, Angles, and Proof

In previous grades, students used facts about supplementary, complementary, vertical, and adjacent angles to solve problems. In previous lessons, students made conjectures, developed definitions of the basic rigid motions, and explained why they think certain claims are true or false. Over the next several lessons, students will learn ways to express their reasoning more formally. In this lesson, students create conjectures about angle relationships and prove them using what they know about rigid transformations. Students begin to label and mark figures to indicate congruence which helps them communicate more precisely. Students are asked to make viable arguments and critique the reasoning of others when they write convincing explanations for why vertical angles are congruent (MP3). This activity includes lesson summary videos and practice problems.

By JOEL NELSON