1. Lesson 2
Lines & Angles
Classifying Angles

2. Warm-Up Draw two adjacent angles named 1 and  2.
Draw an angle that measures 84°.
Solve for x. 4x – 5 = 23
Solve for x. 6x + 11 = 3x + 41

3. Target: Classify angles as acute, right, obtuse or straight.
Classifying Angles
Target: Classify angles as acute, right, obtuse or straight.

4. Vocabulary Acute Angle: An angle that measures more than 0° and less
Right Angle: An angle that measures exactly 90°.
Obtuse Angle: An angle that measures more than 90° but
less than 180°.
Straight Angle: An angle that has a measure of 180°.
Congruent: Equal in measure.

6. Example 1 mJIL = 110° Obtuse mCAT = 64° Acute mFOX = 90° Right
Classify each angle by measuring it with a protractor.
mJIL = 110°
Obtuse
mCAT = 64°
Acute
mFOX = 90°
Right
mDOG = 180°
Straight

7. Example 2
Sketch a diagram of congruent and adjacent angles. The angles share which makes them adjacent. The congruence marks indicate the angles are congruent.

8. Example 3 Use the information in the diagram to write an equation.
Solve for x.
Congruence marks show the angles are congruent.
SIM  PLE
Write the equation x – 11 = 39
Add 11 to each side
5x = 50
Divide by 5 on each side
x = 10

9. Example 4
JAK is congruent to  HIL. The measure of  JAK = (12 – 3x)° and
the measure of  HIL = (44 – x)°. Solve for x. Then find the degree
measure of each angle.
JAK  HIL
Write an equation. 12 – 3x = 44 – x
Add x to both sides x x
12 – 2x = 44
Subtract 12 from each side – – 12
–2x = 32
Divide by – 2 on each side –2 –2
x = –16
Substitute the solution, – 16, for x to find the degree measure of each
angle.
 JAK = 12 – 3(– 16) = = 60°
 HIL = 44 – (– 16) = = 60°

10. Exit Problems Sketch an angle that fits each description.
straight angle
acute angle
right angle
two congruent obtuse angles

11. Communication Prompt
What are other things in math that we might classify?
When would it be important to make sure angles are measured correctly?