1. Objective: Learn to name and classify triangles.

2. There are 3 types of triangles:
Triangles are polygons with 3 sides. They can be classified by the number of congruent (equal) sides they have.
There are 3 types of triangles:
Equilateral Triangles: are triangles that have 3 congruent (equal) sides.
Isosceles Triangles: are triangles that have 2 congruent (equal) sides.
Scalene Triangles: Triangles that have no congruent side.

3. Triangle Cartoon:

4. You can also classify triangles by their angle measures.
Acute Triangles: Triangles in which all angles are acute. All angles are less than 90 degrees.
Right Triangles: is when a triangle has one right angle.
Obtuse Triangles: when the triangle has one obtuse angle.

5. All 3 angles in a triangle add up to 1800.
Steps:
Draw a triangle with a ruler.
Color all the angles.
Cut the triangle.
Cut the 3 corners of your triangle.
Join the 3 angles (corners).
What do they form? _________
Rule: The sum of all angles in a triangle add up to 180 degrees.

6. Examples: Class Example: Find the measure of the unknown angle.
If m<1 = 40, and the m<2 is 70, what is m<3?
Step 1: add the 2 angles given.
Step 2: Subtract the sum from 180º
Your Example:
If the m<1= 35 and the m<J is 115, what is the measurement in <K?

7. Homework: In exercises 1-9: Find the missing angle and write if the triangles are acute, right, or obtuse In exercises 10-15: Write if each triangle is acute, right, or obtuse AND if they are equilateral, isosceles, or scalene.