Saxon Course 2: Lesson 40 (Slides)

Lesson 40

• Sum of the Angle Measures of a Triangle

• Angle Pairs

​Angle Measures of a Triangle

​Remember: a right angle is 90 degrees.

We call this triangle below a right triangle because it contains a right angle.

Let's say angle C measures 45 degrees.

Question: What is the measure of angle A?

​45°

​We just learned that the sum of the angles in a triangle is always 180°. So to find angle A we need to solve 90° + 45° + A = 180°.
180° - 90° - 45° = 45°
Angle A = 45°

​Angle Pairs

- When two angles are side by side

• These angles are also complementary angles. Which means they add up to 90 degrees.

  50° + 40° = 90°

These intersecting lines form 4 angles. 1 and 2 are an example of adjacent angles!

​Vertical angle pairs:

- a pair of non-adjacent angles.

• Vertical Angles always share the same angle measurement!

- Two angles whose sum is 180°.

​120° + 60° = 180°

​Example

• Let's start by solving angle X. Remember that the sum of angles in a triangle is 180°. To find X we will subtract what angle measurements we know: 180° - 90° - 50° = 40°.

• Remember that vertical angles have the same exact measurement. So, angle Z is also equal to 40°.

• To find angle Y, (Remember that a straight angle is 180°) we will just subtract 180 degrees from angle Z's measurement. 180° - 40° = 140°

​Are these angle pairs supplementary or complementary? What do you think?

​Daily Challenge #40

​Homework:

Use lesson or notebook paper.

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