1. Proof Geometry
4-2: Angle Postulates

2. Measuring Angles Angles are measured in degrees
If there are 50° in ABC, we write mABC=50
Note we do not include the degree sign because it is implied by mABC

3. The Angle Measurement Postulate
To every angle, , there corresponds a real number between 0 and 180.
This number is called the measure of , written m .

4. The Angle Construction PostulateH H
mPAB=r

5. Angle Addition PostulateC
If D is in the interior of BAC, then
mBAC = mBAD + mDAC (part + part = whole)

6. Angle Addition Postulate with Subtraction property of equality
Angle addition postulate: mBAC = mBAD + mDAC Sub. Prop. Of eq mDAC mDAC
mBAC - mDAC = mBAD

7. Linear Pair Definition: If and are opposite rays, and
is another ray from the shared vertex A, then
BAC and  CAD form a linear pair C B A D

8. Supplementary angles Definition:
The sum of the measures of two angles is 180,
then the angles are called supplementary

9. The Supplement Postulate
If two angles form a linear pair, then
they are supplementary C B A D

10. Homework
p : # 1-5, 8, 13-16, 21. For 16 write a linear equation involving the measure of the angle x.