Triangle Angles and Their Relationships

This lesson covers the angles of a triangle, focusing on the sum of interior angles and the relationship between interior and exterior angles. The teacher provides examples to solve for unknown angles using these principles. The lesson concludes with a homework assignment for further practice.

What is the sum of the interior angles in any triangle?

• 90 degrees

• 180 degrees

• 360 degrees

• 270 degrees

If two angles of a triangle are known, how can you find the third angle?

• Add the two known angles and subtract from 180 degrees

• Multiply the two known angles

• Divide the sum of the two known angles by 2

• Subtract the two known angles from 360 degrees

In Example 1, what is the measure of angle B if angle A is 14 degrees and angle C is 30 degrees?

• 44 degrees

• 136 degrees

• 96 degrees

• 60 degrees

How do you find the exterior angle X in Example 1?

• Multiply 136 degrees by 2

• Subtract 136 degrees from 180 degrees

• Add 136 degrees to 44 degrees

• Divide 136 degrees by 2

In Example 2, what is the measure of angle X if angle A is 121 degrees?

• 180 degrees

• 39 degrees

• 121 degrees

• 59 degrees

Why is Example 2 considered easier than Example 1?

• It requires no subtraction

• It uses a known adjacent angle directly

• It involves only addition

• It involves fewer calculations

In Example 3, what is the measure of angle A if the exterior angle is 129 degrees?

• 51 degrees

• 129 degrees

• 180 degrees

• 45 degrees

How do you find angle X in Example 3?

• Add 45 degrees and 51 degrees, then subtract from 180 degrees

• Subtract 45 degrees from 180 degrees

• Add 45 degrees and 129 degrees

• Multiply 45 degrees by 51 degrees

What is the measure of angle X in Example 3?

• 84 degrees

• 96 degrees

• 51 degrees

• 45 degrees

What pages are assigned for homework in this lesson?

• Pages 83 to 85

• Pages 79 to 82

• Pages 73 to 75

• Pages 70 to 72