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Perpendicular Bisector
A segment, ray, line, or plane that is perpendicular to a segment at its midpoint.
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Equidistant
A point that is the same distance from two or more other points.
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Distance from a point to a line.
The length of the perpendicular segment from the point to the line.
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Equidistant from the two lines.
A point that is the same distance from one line as it is from another.
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Perpendicular Bisector of a triangle
A line, ray, or segment that is perpendicular to a side of the triangle at the midpoint of the side.
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Concurrent Lines
When three or more lines, rays, or segments intersect in the same point.
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Point of Concurrency
The point of intersection of concurrent lines.
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Circumcenter
The point of concurrecy of the perpendicular bisectors of a triangle. Can lie inside, on, or outside of the triangle.
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Angle bisector of a triangle
A bisector of an angle of the triangle.
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Incenter of the Triangle
The point of concurrency of the angle bisectors.
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Median of a Triangle
A segment whose endpoints are a vertex of the triangle and the midpoint of the opposite side.
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Centroid of the Triangle
The point of concurrency for the medians of a triangle.
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Altitude of a Triangle
The perpendicular segment from a vertex to the opposite side or to the line that contains the opposite side.
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Orthocenter of the Triangle
The point of concurrency of the altitudes of a triangle. Can lie inside, outside, or on the triangle.
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Midsegment of a Triangle
A segment that connects the midpoints of two sides of a triangle.
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Polygon
A plane figure that is formed by three or more segments called sides (no two sides with a commmon endpoint are collinear), and the sides intersect exactly two other sides.
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Vertex
The endpoint of a side of a polygon.
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Convex
A polygon where no line that contains a side of the polygon contains a point in the interior of the polygon.
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Convex
A polygon that contains a side with a point in the interior of the polygon.
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Equilateral
All of the sides of a polygon are congruent.
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Equiangular
All the interior angles are congruent.
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Regular
All of the interior angles of a polygon are congruent and all of the angles are congruent.
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Paralellogram
A quadrilateral with both pairs of opposite sides parallel.
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Rhombus
A parallelogram with four congruent sides.
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Rectangle
A parallelogram with four right angles.
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Square
A parallelogram with four congruent sides and four right angles.
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Trapezoid
A quadrilateral with exactly one pair of parallel sides.
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Isosceles Trapezoid
A trapezoid with congruent legs.
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Kite
A quadrilateral that has two pairs of consecutive congruent sides, but opposite sides are not congruent.
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Image
The figure as a result of a reflection, rotation, or translation.
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Preimage
The original figure before a transformation.
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Transformation
An operation that maps, or moves, the preimage onto the image.
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Isometry
A transformation that preserves lengths. Also preserve angle measures, parallel lines, and distances between points. Also called rigid transformations.
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Reflection
A type of transformation that uses a line like a mirror, with an image reflected over the line.
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Line of Symmetry
A figure in a plane has a line of symmetry if the figure can be mapped onto itself by a reflection in the line.
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Rotation
A transformation in which a figure is turned about a fixed point.
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Center of Rotation
The fixed point about which a figure is turned for a transformation.
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Angle of Rotation
The angle formed from rays drawn from the center of rotation to a point and its image.
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Rotational Symmetry
When a figure can be mapped onto itself by a rotation of 180 degrees or less.
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Translation
A transformation that maps every two points in the plane so that the result is an isometry.
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Vector
A quantity that has both direction and magnitude (size) and is represented by an arrow drawn between two points.
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Initial Point
Starting point of a vector
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Terminal Point
Ending point of a vector, prime
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Component Form
Combines the horizontal and vertical components <5,3>
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Glide Reflection
A transformation in which every point is mapped on to the image by a translation, and then a reflection.
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Composition
Two or more tranformations are combined to produce a single transformation.
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Similar Polygons
When there is a correspondence between two polygons such that their corresponding angles are congruent and the lengths of corresponding sides are proportional.
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Scale factor
The ratio of the lengths of two corresponding sides of similar polygons.
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Dilation
Dilation is a similarity transformation in which a figure is enlarged or reduced using a scale factor ≠ 0, without altering the center.
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Reduction
A dilation where the scale factor is less than one but greater than zero.
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Enlargment
A dilation where the scale factor is greater than one.
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Trigonometric Ratio
A ratio of the lengths of two sides of a right triangle.
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Radius
A segment whose endpoints are the center of the circle and a point on the circle.
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Diameter
A chord that passes through the center of the circle.
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Chord
A segment whose endpoints are on the circle.
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Secant
A line that intersects a circle in two points.
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Tangent
A line in the plane of a circle that intersects the circle in exactly one point.
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Tangent Circles
Coplanar circles that intersect at one point.
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Concentric
Coplanar circles that have a common center.
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Point of Tangency
A point at which a tangent line intersects the circle to which it is tangent.
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Central Angle
An angle whose vertex is the center of a circle.
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Minor Arc
A central angle with a measure of less than 180 degrees.
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Major Arc
A central arc whose measure is greater than 180 degrees.
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Semicircle
The endpoints of an arc are the endpoints of a diameter.
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Inscribed Angle
An angle whose vertex is on a circle adn whose sides contain chords of the circle.
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Intercepted Arc
The arc that lies in the interior of an inscribed angle and has endpoints on the angle.
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