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4.3 to 4.5 Proving Δ s are : SSS, SAS, HL, ASA, & AASPowerPoint Presentation

4.3 to 4.5 Proving Δ s are : SSS, SAS, HL, ASA, & AAS

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### 4.3 to 4.5 Proving Δs are : SSS, SAS, HL, ASA, & AAS

OBJECTIVES

- Use the SSS Postulate
- Use the SAS Postulate
- Use the HL Theorem
- Use ASA Postulate
- Use AAS Theorem

Postulate 19 (SSS)Side-Side-Side Postulate

- If 3 sides of one Δ are to 3 sides of another Δ, then the Δs are .

GIVEN

KL NL,KM NM

PROVE

KLMNLM

Proof

KL NL andKM NM

It is given that

LM LN.

By the Reflexive Property,

So, by the SSS Congruence Postulate,

KLMNLM

EXAMPLE 1:

Use the SSS Congruence Postulate

ACBCAD

1.

GIVEN :

BC AD

ACBCAD

PROVE :

It is given that BC AD By Reflexive property

AC AC, But AB is not congruent CD.

PROOF:

YOUR TURN:

GUIDED PRACTICE

Decide whether the congruence statement is true. Explain your reasoning.

SOLUTION

YOUR TURN (continued):

GUIDED PRACTICE

Therefore the given statement is false and ABC is not

Congruent to CAD because corresponding sides

are not congruent

QPTRST

GIVEN :

QT TR , PQ SR, PT TS

PROVE :

QPTRST

It is given that QT TR, PQ SR, PT TS.So by

SSS congruence postulate, QPT RST. Yes, the statement is true.

PROOF:

YOUR TURN:

GUIDED PRACTICE

Decide whether the congruence statement is true. Explain your reasoning.

SOLUTION

Postulate 20 (SAS)Side-Angle-Side Postulate

- If 2 sides and the included of one Δ are to 2 sides and the included of another Δ, then the 2 Δs are .

BC DA,BC AD

ABCCDA

STATEMENTS

REASONS

S

BC DA

Given

Given

BC AD

BCADAC

A

Alternate Interior Angles Theorem

S

ACCA

Reflexive Property of Congruence

EXAMPLE 2

Example 2:

Use the SAS Congruence Postulate

Write a proof.

GIVEN

PROVE

Example 4 (continued):

Statements_______

1. DR AG; AR GR

2. DR DR

3.DRG & DRA are rt. s

4.DRG DRA

5. Δ DRG Δ DRA

Reasons____________

1. Given

2. Reflexive Property

3. lines form 4 rt. s

4. Right s Theorem

5. SAS Postulate

D

R

G

A

Theorem 4.5 (HL)Hypotenuse - Leg Theorem

- If the hypotenuse and a leg of a right Δ are to the hypotenuse and a leg of a second Δ, then the 2 Δs are .

Postulate 21(ASA):Angle-Side-Angle Congruence Postulate

- If two angles and the included side of one triangle are congruent to two angles and the included side of a second triangle, then the triangles are congruent.

Theorem 4.6 (AAS): Angle-Angle-Side Congruence Theorem

- If two angles and a non-included side of one triangle are congruent to two angles and the corresponding non-included side of a second triangle, then the triangles are congruent.

Proof of the Angle-Angle-Side (AAS) Congruence Theorem

Given:A D, C F, BC EF

Prove: ∆ABC ∆DEF

D

A

B

F

C

Paragraph Proof

You are given that two angles of ∆ABC are congruent to two angles of ∆DEF. By the Third Angles Theorem, the third angles are also congruent. That is, B E. Notice that BC is the side included between B and C, and EF is the side included between E and F. You can apply the ASA Congruence Postulate to conclude that ∆ABC ∆DEF.

E

Is it possible to prove these triangles are congruent? If so, state the postulate or theorem you would use. Explain your reasoning.

Example 5 (continued):

In addition to the angles and segments that are marked, EGF JGH by the Vertical Angles Theorem. Two pairs of corresponding angles and one pair of corresponding sides are congruent. Thus, you can use the AAS Congruence Theorem to prove that ∆EFG ∆JHG.

Is it possible to prove these triangles are congruent? If so, state the postulate or theorem you would use. Explain your reasoning.

Example 6 (continued):

In addition to the congruent segments that are marked, NP NP. Two pairs of corresponding sides are congruent. This is not enough information to prove the triangles are congruent.

Given: AD║EC, BD BC

Prove: ∆ABD ∆EBC

Plan for proof: Notice that ABD and EBC are congruent. You are given that BD BC. Use the fact that AD ║EC to identify a pair of congruent angles.

Example 7 (continued):

Reasons:

- Given
- Given
- If || lines, then alt. int. s are
- Vertical Angles Theorem
- ASA Congruence Postulate

Statements:

- BD BC
- AD ║ EC
- D C
- ABD EBC
- ∆ABD ∆EBC

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