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Geometry
Topic 4 – Congruent Triangles
NOTES – Congruent Figures (4-1)
Definition
Name: _____________________________________________________
Date: _________________________________ Period: ____________
Example
Congruent polygons have congruent
corresponding ________________ and
________________. When you name congruent
polygons, you must list corresponding
________________ in the same order.
THEOREM 4-1 – Third Angles Theorem
Theorem
If…
Then…
If two angles of one triangle are congruent
to two angles of another triangle, then the
________________ angles are ________________.
Finding Congruent Sides & Angles
If ∆𝑊𝑌𝑆 ≅ ∆𝑀𝐾𝑉, what are the congruent corresponding parts?
Using Congruent Sides & Angles
Suppose that ∆𝑊𝑌𝑆 ≅ ∆𝑀𝐾𝑉. If 𝑚∠𝑊 = 62 and 𝑚∠𝑌 = 35, what is 𝑚∠𝑉? Explain.
Finding Congruent Triangles
Is ∆𝐴𝐵𝐷 ≅ ∆𝐶𝐵𝐷? Justify your answer.
(from the
textbook)
Proving Triangles Congruent
̅̅̅̅, ̅̅̅̅̅
̅̅̅̅ ≅ 𝐿𝑂
Given: 𝐿𝑀
𝑀𝑁 ≅ ̅̅̅̅
𝑂𝑁 , ∠𝑀 ≅ ∠𝑂, ∠𝑀𝐿𝑁 ≅ ∠𝑂𝐿𝑁
Prove: ∆𝐿𝑀𝑁 ≅ ∆𝐿𝑂𝑁
STATEMENTS
REASONS
1) ̅̅̅̅
𝐿𝑀 ≅ ̅̅̅̅
𝐿𝑂 , ̅̅̅̅̅
𝑀𝑁 ≅ ̅̅̅̅
𝑂𝑁
̅̅̅̅ ≅ 𝐿𝑁
̅̅̅̅
2) 𝐿𝑁
3) ∠𝑀 ≅ ∠𝑂, ∠𝑀𝐿𝑁 ≅ ∠𝑂𝐿𝑁
4) ∠𝑀𝑁𝐿 ≅ ∠𝑂𝑁𝐿
5) ∆𝐿𝑀𝑁 ≅ ∆𝐿𝑂𝑁
Proving Triangles Congruent
Given: ̅̅̅̅
𝐴𝐸 ≅ ̅̅̅̅
𝐷𝐶 , ̅̅̅̅
𝐸𝐵 ≅ ̅̅̅̅
𝐶𝐵, ̅̅̅̅
𝐵𝐴 ≅ ̅̅̅̅
𝐵𝐷 , ∠𝐴 ≅ ∠𝐷
Prove: ∆𝐴𝐸𝐵 ≅ ∆𝐷𝐶𝐵
STATEMENTS
REASONS
1) ̅̅̅̅
𝐴𝐸 ≅ ̅̅̅̅
𝐷𝐶 , ̅̅̅̅
𝐸𝐵 ≅ ̅̅̅̅
𝐶𝐵 , ̅̅̅̅
𝐵𝐴 ≅ ̅̅̅̅
𝐵𝐷
2)
Given
3) ∠𝐴𝐵𝐸 ≅ ∠𝐷𝐵𝐶
4)
5)
Third Angles Theorem
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