do now 1. ∆ qrs ∆ lmn. name all pairs of congruent corresponding parts. 2.find the equation of...
TRANSCRIPT
Do Now
1. ∆QRS ∆LMN. Name all pairs of congruent corresponding parts.
2. Find the equation of the line through the points (3, 7) and (5, 1)
QR LM, RS MN, QS LN, Q L, R M, S N
y - 1 = -3(x - 5) or y - 7 = -3(x - 3)
or y = -3x + 16
TARGET: SWBAT Prove triangles congruent by using SSS and SAS.
4.2 Triangle Congruence
Example 1: Using SSS to Prove Triangle Congruence
Use SSS to explain why ∆ABC ∆DBC.
It is given that AC DC and that AB DB. By the Reflexive Property of Congruence, BC BC. Therefore ∆ABC ∆DBC by SSS.
Example 2 – More with SSS
Write a Congruence Statement for the following triangles.
It is given that AB CD and BC DA.
By the Reflexive Property of Congruence, AC CA.
So ∆ABC ∆CDA by SSS.
An included angle is an angle formed by two adjacent sides of a polygon.
B is the included angle between sides AB and BC.
It can also be shown that only two pairs of congruent
corresponding sides are needed to prove the
congruence of two triangles if the included angles are also
congruent.
This is Postulate 4-2 (SAS)
The letters SAS are written in that order because the congruent angles must be between pairs of congruent corresponding sides.
Caution
Example 3: Engineering Application
The diagram shows part of the support structure for a tower. Use SAS to explain why ∆XYZ ∆VWZ.
It is given that XZ VZ and that YZ WZ. By the Vertical s Theorem. XZY VZW. Therefore ∆XYZ ∆VWZ by SAS.
Example 4 – More with SAS
Write a Congruence Statement for the following triangles.
It is given that BA BD and ABC DBC. By the Reflexive Property of congruence, BC BC. So ∆ABC ∆DBC by SAS.
Example 5: Proving Triangles Congruent
Given: BC ║ AD, BC AD
Prove: ∆ADB ∆CBD
ReasonsStatements
5. Side-Angle-Side5. ∆ADB ∆ CBD
2. Reflex. Prop. of 1. Given
4. Alt. Int. s Thm.4. CBD ADB
3. Given3. BC || AD
1. BC AD
2. BD BD
Example 6 – More with SAS
Given: QP bisects RQS. QR QS
Prove: ∆RQP ∆SQP
ReasonsStatements
5. Side-Angle-Side5. ∆RQP ∆SQP
4. Reflex. Prop. of
1. Given
3. Def. of bisector3. RQP SQP
2. Given2. QP bisects RQS
1. QR QS
4. QP QP
Assignment #33 - Pages 230-233
Foundation: 1-3, 8, 9, 11-14
Core: 16, 19, 24-26
Lesson Quiz: Part I
Which postulate, if any, can be used to prove the triangles congruent?
1. 2.none SSS
Lesson Quiz: Part II
3. Given: PN bisects MO, PN MO
Prove: ∆MNP ∆ONP
1. Given2. Def. of bisect3. Reflex. Prop. of 4. Given5. Def. of 6. Rt. Thm.7. SAS Steps 2, 6, 3
1. PN bisects MO2. MN ON3. PN PN4. PN MO 5. PNM and PNO are rt. s6. PNM PNO
7. ∆MNP ∆ONP
Reasons Statements