Use Angle Bisectors of Triangles

The figure is an example of a(n) ...

• angle bisector

• perpendicular bisector

• median

• midsegment

What is a line segment or ray drawn from a vertex that divides the angle into two congruent angles?

• Median of a Triangle

• Altitude of a Triangle

• Perpendicular Bisector of a side of a Triangle

• Angle Bisector

• Midpoint of a Line Segment

Find BD.

• BD = 20

• BD = 2

• BD = 4

• BD = 10

Find the length of TU

• 15

• 12

• 26

• 13

What is reason 4?

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What is reason 1?

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Given: m∠LAN = 30⁰ , m∠1 = 15⁰
Prove: AM bisects ∠LAN
Step 1: m∠LAN = 30⁰ 
Step 2: m∠1 + m∠2 = m∠LAN
Step 3: m∠1 + m∠2 = 30⁰
Step 4: m∠1 = 15⁰
Step 5: 15⁰ + m∠2 = 30⁰
Step 6: m∠2 = 15⁰
Step 7: m∠1 = m∠2
What is the justification for Step 7?

• Subtraction property of equality

• Transitive property of equality

• Addition property of equality

• Definition of congruent angles

Given: m∠LAN = 30⁰ , m∠1 = 15⁰
Prove: AM bisects ∠LAN
Step 1: m∠LAN = 30⁰ 
Step 2: m∠1 + m∠2 = m∠LAN
Step 3: m∠1 + m∠2 = 30⁰
Step 4: m∠1 = 15⁰
Step 5: 15⁰ + m∠2 = 30⁰
Step 6: m∠2 = 15⁰
What is the justification for Step 6?

• Subtraction property of equality

• Substitution

• Addition property of equality

• Definition of congruent angles

What is reason 2?

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What is the "statement" for step 2 of the proof?

• ∆BAC≅∆DAC

• BC=DC

• ∡B≅∡D

• ∡BAC≅∡DAC