Download Lesson 4-2 Angles of Triangles Ohio Content

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 twodimensional figures and threedimensional objects.
Theorem 4.1
Angle Sum Theorem
Theorem 4.1
Angle Sum Theorem
The sum of the measures of the
angles of a triangle is 180.
Find the missing angle
measures.
43°
79°
1
74°
2
3
Theorem 4.2
Third Angle Theorem
Theorem 4.2
Third 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
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 4.3
Exterior Angle Theorem
Theorem 4.3
Exterior 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
4
3
38°
32°
2
41°64°
1
29°
Find mA if mC is 20.
B
20°
A
C
Assignment:
Pgs. 189-191
11-35 all,
56-58 evens