Lesson 2 Lines Angles Classifying Angles WarmUp 1

Lesson 2 Lines & Angles Classifying Angles

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

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

Vocabulary � Acute Angle: An angle that measures more than 0° and less than 90°. � 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.

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

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.

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. 5 x – 11 = 39 Add 11 to each side. +11 5 x = 50 Divide by 5 on each side. 5 5 x = 10

Example 4 JAK is congruent to HIL. The measure of JAK = (12 – 3 x)° and the measure of HIL = (44 – x)°. Solve for x. Then find the degree measure of each angle. JAK HIL Write an equation. 12 – 3 x = 44 – x Add x to both sides. +x +x 12 – 2 x = 44 Subtract 12 from each side. – 12 – 2 x = 32 Divide by – 2 on each side. – 2 x = – 16 Substitute the solution, – 16, for x to find the degree measure of each angle. � JAK = 12 – 3(– 16) = 12 + 48 = 60° � HIL = 44 – (– 16) = 44 + 16 = 60°

Exit Problems Sketch an angle that fits each description. 1. straight angle 2. acute angle 3. right angle 4. two congruent obtuse angles

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