Triangle angle properties

7 videos
2 skills
Do the angles in a triangle always add up to the same thing? Would I ask it if they didn't? What do we know about the angles of a triangle if two of the sides are congruent (an isosceles triangle) or all three are congruent (an equilateral)? This tutorial is the place to find out.

Proof: Measures of interior angles of a triangle sum to 180°

VIDEO 6:31 minutes
Sal gives a formal proof that the measures of interior angles of a triangle sum to 180°.

Triangle angle example 1

VIDEO 6:03 minutes
Figuring out angles in a triangle. A little about exterior angles being the sum of the remote interior angles

Triangle angle example 2

VIDEO 4:55 minutes
Another example finding angles in triangles

Triangle angle example 3

VIDEO 5:42 minutes
Multiple ways to solve for the angles of multiple triangles

Challenging triangle angle problem

VIDEO 8:37 minutes
Interesting problem finding the sums of particular exterior angles of an irregular pentagon

Proof: Corresponding angle equivalence implies parallel lines

VIDEO 5:18 minutes
Proof by contradiction that corresponding angle equivalence implies parallel lines

Finding more angles

VIDEO 6:05 minutes
Example of angle hunting!

Finding angle measures 1


Finding angle measures 2