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Five-Minute Check (over Lesson 4–3) Then/Now New Vocabulary Postulate 4.1: Side-Side-Side (SSS) Congruence Example 1: Use SSS to Prove Triangles Congruent Example 2: Standard Test Example Postulate 4.2: Side-Angle-Side (SAS) Congruence Example 3: Real-World Example: Use SAS to Prove Triangles are Congruent Example 4: Use SAS or SSS in Proofs Lesson Menu

A B C D Write a congruence statement for the triangles. A. ΔLMN  ΔRTS B. ΔLMN  ΔSTR C. ΔLMN  ΔRST D. ΔLMN  ΔTRS A B C D 5-Minute Check 1

Name the corresponding congruent angles for the congruent triangles. A. L  R, N  T, M  S B. L  R, M  S, N  T C. L  T, M  R, N  S D. L  R, N  S, M  T A B C D 5-Minute Check 2

Name the corresponding congruent sides for the congruent triangles. A. LM  RT, LN  RS, NM  ST B. LM  RT, LN  LR, LM  LS C. LM  ST, LN  RT, NM  RS D. LM  LN, RT  RS, MN  ST ___ A B C D 5-Minute Check 3

A B C D Refer to the figure. Find x. A. 1 B. 2 C. 3 D. 4 5-Minute Check 4

A B C D Refer to the figure. Find m A. A. 30 B. 39 C. 59 D. 63 5-Minute Check 5

Given that ΔABC  ΔDEF, which of the following statements is true? A. A  E B. C  D C. AB  DE D. BC  FD ___ A B C D 5-Minute Check 6

Use the SSS Postulate to test for triangle congruence. You proved triangles congruent using the definition of congruence. (Lesson 4–3) Use the SSS Postulate to test for triangle congruence. Use the SAS Postulate to test for triangle congruence. Then/Now

included angle Vocabulary

Concept 1

Write a 2-column proof. ___ Given: QU  AD, QD  AU Prove: ΔQUD  ΔADU Use SSS to Prove Triangles Congruent Write a 2-column proof. Given: QU  AD, QD  AU ___ Prove: ΔQUD  ΔADU Example 1

A B C D Write a two-column proof. Given: AC  AB D is the midpoint of BC. Prove: ΔADC  ΔADB ___ A B C D Example 1 CYP

EXTENDED RESPONSE Triangle DVW has vertices D(–5, –1), V(–1, –2), and W(–7, –4). Triangle LPM has vertices L(1, –5), P(2, –1), and M(4, –7). a. Graph both triangles on the same coordinate plane. b. Use your graph to make a conjecture as to whether the triangles are congruent. Explain your reasoning. c. Write a logical argument that uses coordinate geometry to support the conjecture you made in part b. Example 2A

Solve the Test Item a. Example 2B

b. From the graph, it appears that the triangles have the same shapes, so we conjecture that they are congruent. c. Use the Distance Formula to show all corresponding sides have the same measure. Example 2C

Example 2C

Answer:. WD = ML, DV = LP, and VW = PM Answer: WD = ML, DV = LP, and VW = PM. By definition of congruent segments, all corresponding segments are congruent. Therefore, ΔWDV  ΔMLP by SSS. Example 2 ANS

Concept 2

Use SAS to Prove Triangles are Congruent ENTOMOLOGY The wings of one type of moth form two triangles. Write a two-column proof to prove that ΔFEG  ΔHIG if EI  HF, and G is the midpoint of both EI and HF. Example 3

Given: EI  HF; G is the midpoint of both EI and HF. Use SAS to Prove Triangles are Congruent Given: EI  HF; G is the midpoint of both EI and HF. Prove: ΔFEG  ΔHIG 1. 1. EI  HF; G is the midpoint of EI; G is the midpoint of HF. Proof: Reasons Statements 2. 3. 3. FGE  HGI 4. 4. ΔFEG  ΔHIG Example 3

1. Reasons Proof: Statements A B C D 2. 3. 3. ΔABG ΔCGB Example 3

Write a 2-column proof. Prove: Q  S Use SAS or SSS in Proofs Example 4

Write a 2-column proof. A B C D Example 4

End of the Lesson