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BrittanyM
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Acute triangle
A triangle with three acute angles

Auxiliary line
A line drawn in a figure to aid in a proof

Base angle
One of the two angles that have the base of the triangle as a side

Base
The side opposite the vertex angle

Congruent polygons
Two polygons whose corresponding sides and angles are congruent.

Coordinate proof
A style of proof that uses coordinate geometry and algebra.

Corollary
A theorem whose proof follows directly from another theorem

Corresponding angles of polygons
 Angles in the same position in two different polygons that have the same number of
 angles

Corresponding sides of polygons
Sides in the same position in two different polygons that have the same number of sides.

CPCTC
An abbreviation for "Corresponding Parts of Congruent Triangles are Congruent," which can be used as a justification in a proof after two triangles are proven congruent.

Equiangular triangle
A triangle with three congruent angles.

Equilateral triangular
A triangle with three congruent sides

Exterior
The set of all points outside a polygon

Exterior angle
The angle formed by one side of a polygon and the extension of an adjacent side.

Interior
The set of all points inside the figure

Interior angle
The angle formed by two sides of a polygon with a common vertex

Included angle
The angle formed by two adjacent sides of a polygon.

Included side
The common side of two consecutive angles of a polygon.

Isosceles triangle
A triangle with at least two congruent sides.

Leg of an isosceles triangle
One of the two congruent sides of the isosceles triangle.

Obtuse triangle
A triangle with one obtuse angle.

Remote interior angle
An interior angle of a polygon that is not adjacent to the exterior angle.

Right angle
A triangle with one right angle.

Scalene triangle
A triangle with no congruent sides.

Triangle rigidity
A property of triangles that states that if the side lengths of a triangle are fixed, the triangle can have only one shape.

Vertex angle
The intersection of 2 sides of the triangle

Undefined term
A basic figure that is not defined in terms of other figures

Collinear
Points that lie on the same line

Plane
A flat surface that has no thickness and extends forever

