Sum of Angles in Triangles

Triangles classified by sides A scalene triangle has no congruent sides. An isosceles triangle has at least 2 congruent sides An equilateral triangle, all of the sides are congruent.

Triangles classified by angles In an acute triangle, all of the angles are acute. An obtuse triangle has one obtuse angle. A right triangle has one right angle.

Classify each triangle according to its sides and angles. EX1)acute EX2) right isosceles scalene

EX3) acute EX4) right equilateral scalene EX5) obtuse EX6) right isosceles

Tear off the corners of your triangle and put the corners together. The sum of the measures of the angles in a triangle is 180 °. m  1 + m  2 + m  3 = 180 ° 1 3 2

Find the measure of the unknown angle. 55° 80° x 80° + 55° + x = 180° 135° + x = 180° –135° x = 45° EX7) 90° + 2x + x = 180° 90° + 3x = 180° –90° 3x = 90° 90° x 2x EX8) 3 = 3 x = 30° 2x = 60°

Essential Question Describe the process to find the missing angle in a triangle.

Assignment Page

Classify Triangles Classify triangles by the lengths of their sides and their angles. Date ______________

Triangles classified by sides A scalene triangle An isosceles triangle An equilateral triangle,

Triangles classified by angles In an acute triangle An obtuse triangle has A right triangle

Classify each triangle according to its sides and angles. EX1) EX2)

EX3) EX4) EX5) EX6)

Find the measure of the unknown angle. 55° 80° x EX7)

90° 30° x EX8)