Postulate: The Protractor Postulate
Given line AB and a point O on line AB. Consider rays OA and OB,
as well as all the other rays that can be drawn, with O as an
endpoint, on one side of line AB. These rays can be paired with
the real numbers between 0 and 180 in such a way that:
- Ray OA is paired with 0, and ray OB is paired with 180.
- If ray OR is paired with a and ray OQ is paired with b,
then mÐ ROQ = | a - b |.
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