Lesson 4-2
Angles of Triangles
Ohio Content Standards:
Ohio Content Standards:
Establish the validity of conjectures about geometric objects, their properties and relationships by counter-example, inductive and
deductive reasoning, and critiquing arguments made by others.
Ohio Content Standards:
Make and test conjectures about characteristics and properties (e.g.,
sides, angles, symmetry) of two-dimensional figures and three-
dimensional objects.
Theorem 4.1Angle Sum Theorem
Theorem 4.1Angle Sum Theorem
The sum of the measures of the angles of a triangle is 180.
Find the missing angle measures.
43°
3
21
74°
79°
Theorem 4.2Third Angle Theorem
Theorem 4.2Third Angle Theorem
If two angles of one triangle are congruent to two angles of a
second triangle, then the third angles of the triangles are
congruent.
Exterior Angle
Angle formed by one side of a triangle and the extension of
another side.
Exterior Angle
Angle formed by one side of a triangle and the extension of
another side.
1
Remote Interior Angles
Remote Interior Angles
Interior angles of the triangle not adjacent to a given exterior angle.
Remote Interior Angles
Interior angles of the triangle not adjacent to a given exterior angle.
2
3
Theorem 4.3Exterior Angle Theorem
Theorem 4.3Exterior Angle Theorem
The measure of an exterior angle of a triangle is equal to the sum of
the measures of the two remote interior angles.
Find the measure of each numbered angle in the
figure.
5 43
12
29°
38°32°
41° 64°
20. is if Find CmAm B
20°C
A
Assignment:
Pgs. 189-191 11-35 all,
56-58 evens