1. Which side is included between R and F in FTR? 2. Which angles in STU include US? Tell whether you can prove the triangles congruent by ASA or AAS. If you can, state a triangle congruence and the postulate or theorem you used. If not, write not possible. 3. 4. 5. RF S and U Triangle Congruence by ASA and AAS GEOMETRY LESSON 4-3 GHI PQR AAS not possible ABX ACX AAS 4-3
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1.Which side is included between R and F in FTR? 2.Which angles in STU include US? Tell whether you can prove the triangles congruent by ASA or AAS. If.
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1. Which side is included between R and F in FTR?
2. Which angles in STU include US?
Tell whether you can prove the triangles congruent by ASA or AAS. If you can, state a triangle congruence and the postulate or theorem you used. If not, write not possible.
3. 4. 5.
RF
S and U
Triangle Congruence by ASA and AASTriangle Congruence by ASA and AASGEOMETRY LESSON 4-3GEOMETRY LESSON 4-3
CPCTC is an abbreviation for the phrase “Corresponding Parts of Congruent Triangles are Congruent.” It can be used as a justification in a proof after you have proven two triangles congruent because by definition, corresponding parts of congruent triangles are congruent.
SSS, SAS, ASA, AAS, (and HL) use corresponding parts to prove triangles congruent. CPCTC uses congruent triangles to prove corresponding parts congruent.
Work backward when planning a proof. To show that ED || GF, look for a pair of angles that are congruent.
Then look for triangles that contain these angles.
Helpful Hint
ExampleExample
A
B
C LJ
K
Is ABC JKL? YES
What’s the reason? SAS
Example continuedExample continued
A
B
C LJ
K
What other angles are congruent?B K and C L
What other side is congruent?
ABC JKL
BC KL
Example continuedExample continued
A
B
C LJ
K
What other angles are congruent?B K and C L
What other side is congruent?
ABC JKL
BC KL
Example
H J
KL
Prove: H KGiven: HJ || LK and JK || HL
Plan: Show JHL LKJ by ASA, then use CPCTC.
HJL KLJ (Alt Int s)
LJ LJ (Reflexive)
HLJ KJL (Alt Int s)
JHL LKJ (ASA)
H K (CPCTC)
QED
Example 2
A
R
T
M
S
Given: MS || TR and MS TR
Prove: A is the midpoint of MT.
SAM RAT (Vert. s)
SAM RAT (AAS)
Since MS || TR, M T (Alt. Int. s)
MS TR (Given)
MA AT (CPCTC)
A is the midpoint of MT (Def. midpoint)
Plan: Show the triangles are congruent using AAS, then MA =AT. By definition, A is the midpoint of segment MT.
Example 3
P
N L
M
Given: MP bisects LMN and LM NM
Prove: LP NP
NMP LMP (def. bis)
PMN PML (SAS)
QED
MP bis. LMN (Given)
LM NM (Given)
PM PM (Ref)
LP NP (CPCTC)
Given: AB DC, AD BC
Prove: A C
A B
CD
Statements Reasons
1. AB DC 1. Given
2. AD BC 2. Given
3. BD BD 3. Reflexive
4. ABD CDB 4. SSS
5. A C 5. CPCTC
A
B
CE
D
2. A D
3. ACB DCE
4. ACB DCE5. B E
1. AC DC (given)
(given)
(vert s)
(ASA)
(CPCTC)
Show B E
ProofsProofs
Ask: to show angles or segments congruent, what triangles must be congruent?
Then, how do you prove triangles congruent? (SSS, SAS, ASA, AAS)
Prove triangles congruent, then use CPCTC.
What other congruence statements can you prove from the
diagram, in which SL SR, and 1 2 are given? SC SC by the
Reflexive Property of Congruence, and LSC RSC by SAS.
3 4 by corresponding parts of congruent triangles are congruent.
When two triangles are congruent, you can form congruence statements about three pairs of corresponding angles and three pairs of corresponding sides. List the congruence statements.
In the proof, three congruence statements are used, and one congruence statement is proven. That leaves two congruence statements remaining that also can be proved:CLS CRSCL CR
4-4
Quick Check
The Given states that DEG and DEF are right angles.
What conditions must hold for that to be true?
DEG and DEF are the angles the officer makes with the ground.
So the officer must stand perpendicular to the ground, and the ground must be level.