Notes – Lesson 2.5
Geometry
Name ______________________________________
Vertical Angles Theorem.
Find the value of each variable.
1.
4.
2.
3.
5.
6. Proving a theorem.
Given:
 1 and  2 are supplementary.
 3 and  2 are supplementary.
Indirect Proof.
What do we know about
 1 and  2? _______________________________
What do we know about
 3 and  2? ________________________________
So now we can say _____________________ = ________________________ by substitution.
What happens if we subtract
 2 from both sides of the equation, what are we left with? ___________________________
What conclusion can we make? If two angles are _____________________ of the _______________ angle, then the two angles
are ____________________________.
This is the ________________________________________________ Theorem.