Triangles and Angles Classifying Triangles Line segments are

Triangles and Angles

Classifying Triangles • Line segments are congruent if they have the same length • One way to classify triangles is by the number of congruent sides they have

Classifying Triangles • Scalene Triangles have no congruent sides • Isosceles Triangles have two congruent sides • Equilateral Triangles have three congruent sides

Classifying Triangles • Another way to classify triangles is by the measure of their angles • Acute Triangles have three acute angles • Obtuse Triangles have one obtuse angle • Right Triangles have one right angle

Classifying Triangles Checkpoint • Classify each angle by it’s sides and it’s angles: Angle: Acute Angle: Obtuse Angle: Right Side: Scalene Side: Isosceles Equilateral

Interior Angles of a Triangle The sum of the measures of the angles of a triangle is 180

Triangle Mini-Lab Materials Needed: • Pencil • Ruler (share with a neighbor) • Scissors (share with a neighbor) • Protractor

Triangle Mini-Lab • Using a ruler and pencil, draw any large triangle and cut it out with scissors. • Individually label each angle 1, 2, and 3. • Tear off (do NOT cut) a large section of each angle and arrange so each vertex is touching and each angle is adjacent to the next.

Triangle Mini-Lab • What type of angle did the three angles form when placed together? A straight angle • What is the measure of this angle? 180 degrees • Let’s confirm….

Triangle Mini-Lab • Flip over one angle and use your protractor to measure it. • Write the measure on the back of the angle and repeat these steps for the other two angles. • Add up the measures of each of the angles.

Finding The Measures of Angles • In an equilateral triangle, all of the sides are congruent and all of the angle measurements are congruent • What is the measure of each angle?

Finding The Measures of Angles What do we know? • We know that each angle is congruent but we don’t know their measure. Let’s call it “X. ” • We know that all three angles add up to 180 degrees. Therefore, X + X = 180 • What is the measure of each angle? 3 x = 180 X = 60

Finding The Measures of Angles Checkpoint Find the measure of each triangle then classify the triangle by it’s angles: m m m a = 46, b = 42, c = x + 46 + 42 = 180 x + 88 = 180 x = 92 Classify: Obtuse

Finding The Measures of Angles Checkpoint Find the measure of each triangle then classify the triangle by it’s angles: m m m a = 3 x, b = 2 x, c=x 3 x 30 = 90 2 x 30 = 60 x = 30 x + 2 x + 3 x = 180 6 x = 180 x = 30 Classify: Right

Finding The Measures of Angles Checkpoint Find the measure of each triangle then classify the triangle by it’s angles: m m m a = 4 x, b = 3 x, c = 2 x 4 x 20 = 80 3 x 20 = 60 2 x 20 = 40 4 x + 3 x + 2 x = 180 9 x = 180 x = 20 Classify: Acute

Homework • Skill 6: Triangles (both sides) • 6 -2 Practice Skills: Triangles and Angles (both sides) • Due Tomorrow!