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Proving Triangles are Congruent SSS, SAS; ASA; AASPowerPoint Presentation

Proving Triangles are Congruent SSS, SAS; ASA; AAS

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### Proving Triangles are CongruentSSS, SAS; ASA; AAS

### Proving Triangles are Congruent

CCSS: G.CO7

Standards for Mathematical Practices

- 1. Make sense of problems and persevere in solving them.
- 2. Reason abstractly and quantitatively.
- 3. Construct viable arguments and critique the reasoning of others.
- 4. Model with mathematics.
- 5. Use appropriate tools strategically.
- 6. Attend to precision.
- 7. Look for and make use of structure.
- 8. Look for and express regularity in repeated reasoning.

CCSS:G.CO 7

- USE the definition of congruence in terms of rigid motions to SHOW that two triangles ARE congruent if and only if corresponding pairs of sides and corresponding pairs of angles ARE congruent.

ESSENTIAL QUESTION

- How do we show that triangles are congruent?
- How do we use triangle congruence to plane and write proves ,and prove that constructions are valid?

Objectives:

- Prove that triangles are congruent using the ASA Congruence Postulate and the AAS Congruence Theorem
- Use congruence postulates and theorems in real-life problems.

Proving Triangles are Congruent:

SSS and SAS

SSS AND SASCONGRUENCE POSTULATES

then

If

1.ABDE

4.AD

2.BCEF

5. BE

ABCDEF

3.ACDF

6.CF

If all six pairs of corresponding parts (sides and angles) are

congruent, then the triangles are congruent.

Sides are

congruent

Angles are

congruent

Triangles are

congruent

and

SSS AND SASCONGRUENCE POSTULATES

S

S

S

Side MNQR

then MNPQRS

Side NPRS

Side PMSQ

POSTULATE

POSTULATE 19Side -Side -Side (SSS) Congruence Postulate

If three sides of one triangle are congruent to three sidesof a second triangle, then the two triangles are congruent.

If

SSS AND SASCONGRUENCE POSTULATES

The SSS Congruence Postulate is a shortcut for provingtwo triangles are congruent without using all six pairsof corresponding parts.

SSS AND SASCONGRUENCE POSTULATES

POSTULATE

Side PQWX

A

S

S

then PQSWXY

Angle QX

Side QSXY

POSTULATE 20Side-Angle-Side (SAS) Congruence Postulate

If two sides and the included angle of one triangle are

congruent to two sides and the included angle of a

second triangle, then the two triangles are congruent.

If

Congruent Triangles in a Coordinate Plane

AC FH

ABFG

Use the SSS Congruence Postulate to show that ABCFGH.

SOLUTION

AC = 3 and FH= 3

AB = 5 and FG= 5

Congruent Triangles in a Coordinate Plane

d = (x2 – x1 )2+ (y2 – y1 )2

d = (x2 – x1 )2+ (y2 – y1 )2

BC = (–4 – (–7))2+ (5– 0)2

GH = (6 – 1)2+ (5– 2)2

= 32+ 52

= 52+ 32

= 34

= 34

Use the distance formula to find lengths BC and GH.

Congruent Triangles in a Coordinate Plane

BCGH

BC = 34 and GH= 34

All three pairs of corresponding sides are congruent,

ABCFGH by the SSS Congruence Postulate.

SAS postulate

SSS postulate

C

S

G

The vertex of the included angle is the point in common.

SSS postulate

SAS postulate

SSS postulate

Not enough info

SSS postulate

SAS postulate

SAS postulate

SSS postulate

Not Enough Info

SAS postulate

SAS postulate

Congruent Triangles in a Coordinate Plane

MN DE

PMFE

Use the SSS Congruence Postulate to show that NMPDEF.

SOLUTION

MN = 4 and DE= 4

PM = 5 and FE= 5

Congruent Triangles in a Coordinate Plane

d = (x2 – x1 )2+ (y2 – y1 )2

d = (x2 – x1 )2+ (y2 – y1 )2

PN = (–1 – (– 5))2+ (6– 1)2

FD = (2 – 6)2+ (6– 1)2

= 42+ 52

= (-4)2+ 52

= 41

= 41

Use the distance formula to find lengths PN and FD.

Congruent Triangles in a Coordinate Plane

PNFD

PN = 41 and FD= 41

All three pairs of corresponding sides are congruent,

NMPDEF by the SSS Congruence Postulate.

ASA; AAS

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.

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

Theorem 4.5: Angle-Angle-Side (AAS) Congruence TheoremGiven: congruent to two angles and the corresponding non-included side of a second triangle, then the triangles are congruent.A D, C F, BC EF

Prove: ∆ABC ∆DEF

Theorem 4.5: Angle-Angle-Side (AAS) Congruence TheoremYou are given that two angles of congruent to two angles and the corresponding non-included side of a second triangle, then the triangles are congruent.∆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.

Theorem 4.5: Angle-Angle-Side (AAS) Congruence TheoremIs it possible to prove the triangles are congruent? If so, state the postulate or theorem you would use. Explain your reasoning.

Ex. 1 Developing ProofA. In addition to the angles and segments that are marked, state the postulate or theorem you would use. Explain your reasoning.EGF JGH by the Vertical Angles Theorem. Two pairs of corresponding angles and one pair of corresponding sides are congruent. You can use the AAS Congruence Theorem to prove that ∆EFG ∆JHG.

Ex. 1 Developing ProofIs it possible to prove the triangles are congruent? If so, state the postulate or theorem you would use. Explain your reasoning.

Ex. 1 Developing ProofB. 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.

Ex. 1 Developing ProofIs it possible to prove the triangles are congruent? If so, state the postulate or theorem you would use. Explain your reasoning.

UZ ║WX AND UW

║WX.

Ex. 1 Developing Proof1

2

3

4

The two pairs of parallel sides can be used to show state the postulate or theorem you would use. Explain your reasoning.1 3 and 2 4. Because the included side WZ is congruent to itself, ∆WUZ ∆ZXW by the ASA Congruence Postulate.

Ex. 1 Developing Proof1

2

3

4

Given: AD state the postulate or theorem you would use. Explain your reasoning.║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.

Ex. 2 Proving Triangles are CongruentStatements: state the postulate or theorem you would use. Explain your reasoning.

BD BC

AD ║ EC

D C

ABD EBC

∆ABD ∆EBC

Reasons:

1.

Proof:Statements: state the postulate or theorem you would use. Explain your reasoning.

BD BC

AD ║ EC

D C

ABD EBC

∆ABD ∆EBC

Reasons:

1. Given

Proof:Statements: state the postulate or theorem you would use. Explain your reasoning.

BD BC

AD ║ EC

D C

ABD EBC

∆ABD ∆EBC

Reasons:

Given

Given

Proof:Statements: state the postulate or theorem you would use. Explain your reasoning.

BD BC

AD ║ EC

D C

ABD EBC

∆ABD ∆EBC

Reasons:

Given

Given

Alternate Interior Angles

Proof:Statements: state the postulate or theorem you would use. Explain your reasoning.

BD BC

AD ║ EC

D C

ABD EBC

∆ABD ∆EBC

Reasons:

Given

Given

Alternate Interior Angles

Vertical Angles Theorem

Proof:Statements: state the postulate or theorem you would use. Explain your reasoning.

BD BC

AD ║ EC

D C

ABD EBC

∆ABD ∆EBC

Reasons:

Given

Given

Alternate Interior Angles

Vertical Angles Theorem

ASA Congruence Theorem

Proof:Note: state the postulate or theorem you would use. Explain your reasoning.

- You can often use more than one method to prove a statement. In Example 2, you can use the parallel segments to show that D C and A E. Then you can use the AAS Congruence Theorem to prove that the triangles are congruent.

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