Step 7 Objective

Identify alternate and corresponding angles; understand a proof that the sum of the angles of a triangle is 180° and of a quadrilateral is 360°.


Probing questions

How could you convince me that the sum of the angles of a triangle is 180°?

Why are parallel lines important when proving the sum of the angles of a triangle?

How does knowing the sum of the angles of a triangle help you to find the sum of angles of a quadrilateral? Will this work for all quadrilaterals? Why?