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Chapter 4.2 Notes: Apply Congruence and Triangles. Goal: You will identify congruent figures. Two geometric figures are congruent if they have exactly the same size and shape. Congruence Statements
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Chapter 4.2 Notes: Apply Congruence and Triangles Goal: You will identify congruent figures.
Two geometric figures are congruent if they have exactly the same size and shape. Congruence Statements • In two congruent figures, all the parts of one figure are congruent to the corresponding parts of the other figure. • In congruent polygons, this means that the corresponding sides and the corresponding angles are congruent.
Identifying congruent figures • Two geometric figures are congruent if they have exactly the same size and shape. NOT CONGRUENT CONGRUENT
Corresponding angles A ≅ P B ≅ Q C ≅ R Corresponding Sides AB ≅ PQ BC ≅ QR CA ≅ RP Triangles B Q R A C P
Ex.1: Write a congruence statement for the triangles. Identify all pairs of congruent corresponding parts.
Ex.2: In the diagram, . a. Find the value of x. b. Find the value of y.
Ex.3: In the diagram below, . a. Identify all pairs of congruent corresponding parts. b. Find the value of x and find .
Ex.4: Show that . • Theorem 4.3 Third Angles Theorem: If two angles of one triangle are congruent to two angles of another triangle, then the third angles are also congruent.
Find the value of x. In the diagram, N ≅ R and L ≅ S. From the Third Angles Theorem, you know that M ≅ T. So mM = mT. From the Triangle Sum Theorem, mM=180° - 55° - 65° = 60° mM = mT 60° = (2x + 30)° 30 = 2x 15 = x Ex. 3 Using the Third Angles Theorem (2x + 30)° 55° 65°
Ex.5: Find . Ex.6: In the diagram, what is ?
Ex.7: The two triangles are congruent. Identify all angles and sides that are congruent. Then write a congruence statement.
Ex.8: In the diagram, a. Find the value of x. b. Find the value of y.
Properties of Congruent Triangles • Theorem 4.4 Properties of Congruent Triangles: • Reflexive Property of Congruent Triangles: For any triangle ABC, . • Symmetric Property of Congruent Triangles: If , then . • Transitive Property of Congruent Triangles: If , then .