Exploring Interior Angles of Triangles

Mrs. Holly teaches eighth-grade students about the interior angles of triangles. The lesson covers basic and complex problems, including solving for unknown angles using the sum of interior angles, which equals 180 degrees. Examples include triangles BCD, GHI, ABC, and additional problems with triangles X and Y. Students are encouraged to practice and submit answers via a Google form.

What is the goal of today's lesson?

• To find the area of triangles

• To find the perimeter of triangles

• To find the measure of interior angles of triangles

• To find the measure of exterior angles of triangles

What is the sum of the interior angles of a triangle?

• 360 degrees

• 270 degrees

• 180 degrees

• 90 degrees

In the first example, if two angles of a triangle are 40 degrees each, what is the measure of the third angle?

• 60 degrees

• 100 degrees

• 80 degrees

• 120 degrees

In the second example, if one angle is 105 degrees and another is 40 degrees, what is the measure of the third angle?

• 40 degrees

• 25 degrees

• 30 degrees

• 35 degrees

In the challenge problem, if angle A is 3x + 28 degrees, angle B is 5x + 52 degrees, and angle C is 2x - 10 degrees, what is the value of x?

• 12

• 10

• 9

• 11

What is the measure of angle A in the challenge problem if x equals 11?

• 61 degrees

• 64 degrees

• 62 degrees

• 63 degrees

What is the measure of angle B in the challenge problem if x equals 11?

• 105 degrees

• 106 degrees

• 107 degrees

• 108 degrees

In the final example, if x equals 40, what is the measure of the angle represented by X + 21?

• 61 degrees

• 50 degrees

• 55 degrees

• 60 degrees

In the final example, if x equals 40, what is the measure of the angle represented by 3x - 18?

• 107 degrees

• 105 degrees

• 102 degrees

• 110 degrees

In the final example, if x equals 40, what is the measure of the angle represented by x - 9?

• 31 degrees

• 32 degrees

• 30 degrees

• 29 degrees