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Congruent Figures

 H  E.  S  T,. WA NO, AS OT, SH TE, WH NE;  W  N,.  A  O,. Sample: DFH ZPR. Sample: ABD CDB.

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Congruent Figures

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  1. H E S T, WA NO, AS OT, SH TE, WH NE; W N, A O, Sample: DFHZPR Sample: ABDCDB Sample: Two pairs of corresponding sides and two pairs of corresponding angles are given. C A because all right angles are congruent. BDBD by the Reflexive Property of . ABDCDB by the definition of congruent triangles. Congruent Figures GEOMETRY LESSON 4-1 In Exercises 1 and 2, quadrilateral WASH quadrilateral NOTE. 1. List the congruent corresponding parts. 2.mO = mT = 90 and mH = 36. Find mN. 3. Write a statement of triangle congruence.4. Write a statement of triangle congruence.5. Explain your reasoning in Exercise 4 above. 144 4-1

  2. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 (For help, go to Lesson 2-5.) What can you conclude from each diagram? 1.2.3. 2. The two triangles share a side, so PRPR. According to the tick marks on the angles, QPR SRP and Q  S. 3. According to the tick marks on the sides, TO NV. The tick marks on the angles show that MS. Since MO || VS, by the Alternate Interior Angles Theorem MON SVT. Since OV OV by the Reflexive Property, you can use the Segment Addition Property to show TVNO. 1. According to the tick marks on the sides, ABDE. According to the tick marks on the angles, CF. Check Skills You’ll Need 4-2

  3. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 The property of triangle rigidity gives you a shortcut for proving two triangles congruent. It states that if the side lengths of a triangle are given, the triangle can have only one shape. 4-2

  4. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 For example, you only need to know that two triangles have three pairs of congruent corresponding sides. This can be expressed as the following postulate. 4-2

  5. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 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. 4-2

  6. An included angle is an angle formed by two adjacent sides of a polygon. B is the included angle between sides AB and BC. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 4-2

  7. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 4-2

  8. Caution The letters SAS are written in that order because the congruent angles must be between pairs of congruent corresponding sides. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 4-2

  9. SSA: Side-Side-Angle • THIS DOES NOT WORK! • It is a very common trap and students fall for it easily. • Example: are these triangles congruent? NO! SSA S S A A S S

  10. Why doesn’t it work?

  11. Why doesn’t it work? These triangles are not congruent even though two sides and an angle are congruent.

  12. Don't make an out of yourself. Don't use SSA!

  13. Decide if the following triangles are congruent using SSS or SAS.

  14. Use SSS or SAS. •  by SSS X Y S S S S S Z W

  15. Not  (uses SSA) E S S A S A T M A

  16.  by SAS L S A S J K A S H

  17.  by SAS A S S S A A K S S D T

  18. Not  (uses SSA) E L S S A A S S O N V

  19.  by SSS S S S S S

  20. Summary • To prove two triangles are congruent use SSS or SAS

  21. Given:M is the midpoint of XY, AXAY Prove: AMXAMY Copy the diagram. Mark the congruent sides. You are given that M is the midpoint of XY, and AXAY. Midpoint M implies MXMY. AMAM by the Reflexive Property of Congruence, so AMXAMY by the SSS Postulate. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 Using SSS Write a paragraph proof. Quick Check 4-2

  22. It is given that ADBC. Also, DCCD by the Reflexive Property of Congruence. You now have two pairs of corresponding congruent sides. Therefore if you know ADCBCD, you can prove ADCBCD by SAS. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 Using SAS ADBC. What other information do you need to prove ADCBCD by SAS? Quick Check 4-2

  23. Copy the diagram. Mark what is given on the diagram. It is given that RSGRSH and SGSH. RSRS by the Reflexive Property of Congruence. Two pairs of corresponding sides and their included angles are congruent, so RSGRSH by the SAS Postulate. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 Are the Triangles Congruent? Quick Check Given: RSGRSH, From the information given, can you prove RSG  RSH? Explain. 4-2

  24. BG and BV APB XPY; SAS If you know DO DG, the triangles are by SSS; if you know DWO DWG, they are by SAS. No; corresponding angles are not between corresponding sides. Triangle Congruence by SSS and SAS GEOMETRY LESSON 4-2 1. In VGB, which sides include B? 2. In STN, which angle is included between NS and TN? 3. Which triangles can you prove congruent? Tell whether you would use the SSS or SAS Postulate. 4. What other information do you need to prove DWODWG? 5. Can you prove SEDBUT from the information given? Explain. N 4-2

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