1. 4.1 Triangle Angle Sum and Properties

2. How many degrees in a triangle? The sum of the angles in any triangle is exactly 180 degrees

3. Classify Triangles by Angles Right - having one angle of 90 degrees Obtuse – having one angle over 90 degrees Acute – having all its angles under 90 degrees

4. Classify triangles by side Equilateral – all the sides are the same length Isosceles – Two sides are the same length Scalene – No sides are the same length

5. Interior and Exterior angles Interior angles are in red Exterior angles are in yellow

6. Exterior angle Theorem How much is X ? Notice that the value of X is the same as the sum of the 50 and 60 degree angles!

7. Exterior Angle Theorem An exterior angle of a triangle is always equal to the sum of the interior angles that are not adjacent to it.

8. Find X

9. Acute Angles of a Right Triangles The acute angles of a right triangle are always complementary