1. By: Natalie Alexander

2. Vocab Angle Addition Postulate – Adding two angles creates a larger angle.

3. Finding an Angle Measure

4. Angle Addition Postulate To solve an angle addition postulate, write an equation to find the value of x. Substitute in angle values. A B C D (2x+10)˚ (4x-3)˚ Angle ABC = Angle ABD + Angle DBC Angle ABC = 145˚ 145˚ = (2x+10)˚ + (4x-3)˚

5. Angle Addition Postulate Combine the like terms in your new equation. Angle ABC = 145˚ (2x+10)˚ (4x-3)˚ A B C D 145˚ = (2x+10)˚ + (4x-3)˚145˚ = (6x+7)˚

6. Angle Addition Postulate Solve your new equation. 145˚ = (6x+7)˚ -7 138˚ = 6x 6 6 23 = x

7. Angle Addition Postulate Substitute your answer for x. (2x+10)˚ 92-3˚ Angle ABC = 145˚ A D C B 23 = x 46+10˚ (4x-3)˚

8. Angle Addition Postulate Now, just add. Angle ABC = 145˚ A B C D 46+10˚ 92-3˚ 23 = x 56˚ 89˚

9. Double an Angle Measure

10. Angle Addition Postulate To double an angle measure, first write an equation for x. We know that ray XZ bisects angle WXY, so… X W Y Z 18˚ Angle WXY = Angle WXZ + Angle ZXY Angle WXY = 18 ˚ + Angle ZXY

11. Angle Addition Postulate Since we know ray XZ is a bisector, angle ZXY must be the same as angle WXZ. Angle WXY = 18 ˚ + Angle ZXY W X Z Y 18˚ 36˚ = 18˚ + 18˚ 18˚ Angle WXY = 36˚

12. Thank you for watching!

13. Citations: McDougal Littel Geometry Textbook