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

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