Question

What is the reason for step 5 in this proof?



Alternate Exterior Angles Theorem



angle addition and definition of a straight angle



Corresponding angles of congruent triangles are congruent.



definition of supplementary angles



Done


Given: ΔABC (view diagram)
Prove: The sum of the interior angle measures of ΔABC is 180°.



Statement


Reason


1. Let points A, B, and C form a triangle.

given


2. Let DE←→ be a line passing through B,
parallel to AC¯¯¯¯¯, with angles as labeled.

defining a parallel line and labeling angles

Answer 1

Where is the diagram?
Where is the rest of the proof?