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acute triangle

a triangle whose interior angles are all acute

auxiliary line

line (or ray or segment) added to a diagram to help in a proof

base angles

the angles whose vertices are the endpoints of the base of the triangle

congruence transformation

Transformation that changes the position of the figure without changing its size or shape. Rotation, Translation or Reflection.

congruent polygons

polygons with same size and shape

coordinate proof

A proof involving placing geometric figures in a coordinate plane.


(logic) an inference that follows directly from the proof of another proposition

corresponding parts

Sides or angles that occupy the same relative positions in similar polygons.

equiangular triangle

A triangle with 3 congruent angles

equilateral triangle

a triangle with three congruent sides

exterior angle

An angle formed by one side of a polygon and the extension of an adjacent side

flow proof

a type of proof that uses arrows to show flow of a logical argument statements are connected by arrows to show how each statement comes before it. and each reason is written below the statement it justifies

included angle

An angle created by two adjacent sides

included side

the common side of two consecutive angles of a polygon

isosceles triangle

a triangle with two equal sides

obtuse triangle

a triangle that contains an obtuse interior angle


A transformation that "flips" a figure over a mirror or reflection line.

remote interior angles

the two nonadjacent interior angles corresponding to each exterior ange of a triangle

right triangle

a triangle with one right angle


(mathematics) a transformation in which the coordinate axes are rotated by a fixed angle about the origin

scalene triangle

a triangle with no two sides of equal length


(mathematics) a transformation in which the origin of the coordinate system is moved to another position but the direction of each axis remains the same

vertex angle

the angle in a triangle opposite the base

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