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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.