Using Parts of Congruent Triangles to Find x, Sides, and Angles. Exterior Angle Theorem.

You have been told that two triangles are congruent. Now, the issue is: How may you use this congruence statement to find x, and one side, or angle? Do you have to equal expressions, or do you setup an equation equal to 180°?

Have you heard about the Exterior Angle Theorem? Do you know what are remote interior angles? How is the exterior angle related to the remote interior angles?

You will really enjoy working this lesson. It will show you some examples about Exterior Angle Theorem, and It will present you Corresponding Parts of Congruent Triangles are Congruent, and then it builds on CPCTC to show you a set of examples like the ones above described. For each couple of examples; you will be given a problem to solve using your stylus and the marker tools menu right there on the screen of your device. You will know if your answer is right, or wrong right away!

Lesson's Content

Lesson In PDF Format (no animations)


Lesson's Glossary

Acute angle
An angle whose measure is greater than 0 but less than 90 degrees.

Acute triangle
A triangle whose angles are acute.


Corresponding Parts of Congruent Triangles are Congruent.

Equilateral triangle
A triangle whose sides are equal in length.

Isosceles triangle
A triangle with two sides of equal length.

Obtuse angle
An angle whose measure is greater than 90 but less than 180 degrees.

Obtuse triangle
A triangle with one acute angle.

Right triangle
A triangle that has a 90 degree angle.

Scalene triangle
A triangle with no equilateral sides.

A polygon with three sides.


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