TrianglesToday you will learn to:

• classify triangles by angles and sides.

M07.C-G.1.1.2: Identify or describe the properties of all types of triangles based on angle and side measures.

M07.C-G.1.1.3: Use and apply the triangle inequality theorem.

Warm-up Problem: Warm-up Problem: TrianglesTriangles

Bobby planned to retile the backsplash behind his range in his kitchen, and wanted to follow the pattern shown below. If BI and BJ are the same length, and JI is half the length of BI and BJ, what type of triangle is ΔJBI? What would the measure of angle x be?

TrianglesA triangle is a figure formed by three line

segments, or parts of a line containing two endpoints, that intersect only at their endpoints.

The sum of the measures of the angles of a triangle is 180°.

Each pair of segments forms an angle of the triangle.

The vertex of each angle is a vertex of the triangle. Vertices is the plural of vertex.

Classify Triangles by their ANGLES or their SIDES

Angle Measures of Triangles

Look at the triangle to the right. If we were to add each angle, it should equal 180.

55 + 80 + 45 = 180

Follow this format when determining the value of a missing angle and/or variable in a triangle:

L1 + L2 + L3 = 180

Angle Measures of Triangles: Examples

Find the value of x in triangle ΔABC.

L1 + L2 + L3 = 180 x + x + 102 = 180 2x+ 102 = 1802x+ 102 - 102 = 180 -

102 2x / 2 = 78 / 2

x = 39

Angle Measures of Triangles: Examples