formed by one side of the triangle and the extension of an adjacent side. Each exterior angle has two remote interior angles
Remote interior angle
interior angle that is not adjacent to the exterior angle
Corresponding angles + Corresponding sides
the same position in polygons with an equal number of sides
Congruent polygons
(example) Two polygons are congruent polygons if and only if their corresponding angles and sides are congruent. Thus triangles that are the same size and shape are congruent
Triangle rigidity
provides a shortcut for proving two triangles congruent. (example) It states that if the side lengths of a triangle are given, the triangle can only have one shape
Included angle
Angle formed by two adjacent sides of a polygon
Included side
Common side of two consecutive angles in a polygon
Angle-Side-Angle (ASA)
If two angles and the included side of one triangle are congruent to two angles and the included side of another triangle, then the triangles are congruent
Hypotenuse-Leg (HL)
If the hypotenuse and a leg of a right triangle are congruent to the hypotenuse and a leg of another right triangle, then the triangles are congruent
CPCTC - abbreviation for the phrase “Corresponding Parts of Congruent Triangles are Congruent.”
Can be used as a justification in a proof after you have proven two triangles congruent
Coordinate proof
A style of proof that uses coordinate geometry and algebra. The first step of a coordinate proof is to position the given figure in the plane