Lesson 2: 3.2 Triangle Angle Sum
Duration of Days: 4
Lesson Objective
Prove and apply the 180° interior angle sum theorem
Why do the interior angles of every triangle always add up to exactly 180 degrees?
Interior sum
Exterior angle
CCSS.G.CO.C.10
I DO: Draw a triangle on paper, rip off the three corners, and paste them together to show they form a flat 180° line.
WE DO: "Puzzle solving" on the whiteboard, finding the missing 3rd angle when two are provided.
YOU DO: Complete a worksheet solving for missing angles in various orientations.
Provide a visual proof for a foundational math rule.
DOK 2
Support (Low): Allow calculator use for all subtraction (180 - a - b)
Formative Assessment
Paper triangles
scissors
glue