Download 4.2

Solve for x and y:
y°
43°
75°
x and 43° are Alternate Interior
Angles
43° = x
z°
x°
• 75° = y + 43°
• 75 – 43 = y
• 32° = y
4.2 Congruence and Triangles
Objective: Show that figures are
congruent and identify
corresponding parts of congruent
triangles
What are the corresponding parts
• Given that ABC≅ DEF
• Name all corresponding parts
Congruence Statements
• When you write a
congruence statement
for two polygons,
always list the
corresponding vertices
in the same order.
ABC≅ DEF
<CBA ≅ <FED
Name the other
congruent parts.
Theorem 4.3: Third Angle Theorem
Statement
Reason
<B≅<I and <A≅<H
Given
m<C = 57°
Triangle Sum Theorem
m<J = 57°
Triangle Sum Theorem
<C ≅ <J
Definition of Congruent Angles
Properties of Congruent Triangles
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Reflexive Property of Congruent Triangles
ABC ≅ ABC
Symmetric Property of Congruent Triangles
If ABC ≅ DEF then DEF ≅ ABC
Transitive Property of Congruent Triangles
If ABC ≅ DEF and DEF ≅ JKL
Then ABC ≅ JKL
What must you show to prove two
triangles are congruent
• All three angles in one triangle must be
congruent to the three angles in the second
triangle
• All three sides must be congruent to the three
sides of the second triangle
Homework
11/4
4.2
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