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Warm Up

Warm Up. Lesson Presentation. Lesson Quiz. Warm Up Classify each angle as acute, obtuse, or right. 1. 2. 3. 4. If the perimeter is 47, find x and the lengths of the three sides. right. acute. obtuse. x = 5; 8; 16; 23. Homework: Page 410-411 You should be done with 1-16

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Warm Up

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  1. Warm Up Lesson Presentation Lesson Quiz

  2. Warm Up Classify each angle as acute, obtuse, or right. 1. 2. 3. 4. If the perimeter is 47, find x and the lengths of the three sides. right acute obtuse x = 5; 8; 16; 23

  3. Homework: Page 410-411 You should be done with 1-16 For Tonight work on Problems#: 16*, 22, 23 Include a graph for each problem, use a ruler & compass!

  4. An auxiliary line is a line that is added to a figure to aid in a proof. An auxiliary line used in the Triangle Sum Theorem

  5. The interior is the set of all points inside the figure. The exterior is the set of all points outside the figure. Exterior Interior

  6. An interior angle is formed by two sides of a triangle. An exterior angle is formed by one side of the triangle and extension of an adjacent side. 4 is an exterior angle. Exterior Interior 3 is an interior angle.

  7. Each exterior angle has two remote interior angles. A remote interior angle is an interior angle that is not adjacent to the exterior angle. The remote interior angles of 4 are 1 and 2. Exterior Interior 4 is an exterior angle. 3 is an interior angle.

  8. Objectives Apply SSS and SAS to construct triangles and solve problems. Prove triangles congruent by using SSS and SAS.

  9. Vocabulary triangle rigidity included angle

  10. The property of triangle rigidity states that if the side lengths of a triangle are given, the triangle can have only one shape.

  11. 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.

  12. Remember! Adjacent triangles share a side, so you can apply the Reflexive Property to get a pair of congruent parts.

  13. It is given that AC DC and that AB  DB. By the Reflexive Property of Congruence, BC  BC. Therefore ∆ABC  ∆DBC by SSS. Example 1: Using SSS to Prove Triangle Congruence Use SSS to explain why ∆ABC  ∆DBC.

  14. It is given that AB CD and BC  DA. By the Reflexive Property of Congruence, AC  CA. So ∆ABC  ∆CDA by SSS. TEACH! Example 1 Use SSS to explain why ∆ABC  ∆CDA.

  15. An included angle is an angle formed by two adjacent sides of a polygon. B is the included angle between sides AB and BC.

  16. 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.

  17. Caution The letters SAS are written in that order because the congruent angles must be between pairs of congruent corresponding sides.

  18. It is given that XZ VZ and that YZ  WZ. By the Vertical s Theorem. XZY  VZW. Therefore ∆XYZ  ∆VWZ by SAS. Example 2: Engineering Application The diagram shows part of the support structure for a tower. Use SAS to explain why ∆XYZ  ∆VWZ.

  19. It is given that BA BD and ABC  DBC. By the Reflexive Property of , BC  BC. So ∆ABC  ∆DBC by SAS. TEACH! Example 2 Use SAS to explain why ∆ABC  ∆DBC.

  20. The SAS Postulate guarantees that if you are given the lengths of two sides and the measure of the included angles, you can construct one and only one triangle.

  21. 1.BC || AD 3. BC  AD 4. BD BD Proving Triangles Congruent Given: BC║ AD, BC AD Prove: ∆ABD  ∆CDB Statements Reasons 1. Given 2. CBD  ADB 2. Alt. Int. s Thm. 3. Given 4. Reflex. Prop. of  5.∆ABD  ∆CDB 5. SAS Steps 3, 2, 4

  22. 2.QP bisects RQS 1. QR  QS 4. QP  QP TEACH! Proving Triangles Congruent Given: QP bisects RQS. QR QS Prove: ∆RQP  ∆SQP Statements Reasons 1. Given 2. Given 3. RQP  SQP 3. Def. of bisector 4. Reflex. Prop. of  5.∆RQP  ∆SQP 5. SAS Steps 1, 3, 4

  23. 26° ABC  DBC BC  BC AB  DB So ∆ABC  ∆DBC by SAS Lesson Quiz: Part I 1. Show that∆ABC  ∆DBC, when x = 6. Which postulate, if any, can be used to prove the triangles congruent? 3. 2. none SSS

  24. Statements Reasons 1.PN bisects MO 2.MN  ON 3.PN PN 4.PN MO 5.PNM and PNO are rt. s 6.PNM  PNO 7.∆MNP  ∆ONP 1. Given 2. Def. of bisect 3. Reflex. Prop. of  4. Given 5. Def. of  6. Rt.   Thm. 7. SAS Steps 2, 6, 3 Lesson Quiz: Part II 4. Given: PN bisects MO,PN  MO Prove: ∆MNP  ∆ONP

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