COORDINATE If a point A is located at a certain real number on a scaled number line, then that real number is the coordinate of the point A.
DISTANCE If two points, A and B, are located on a number line, then the positive difference of their coordinates is the distance between A and B.
LINE SEGMENT If points A and B are on line l, then the line segment determined by A and B are the endpoints A and B combined with all of the points between A and B.
ENDPOINTS The endpoints of the line segment determined by A and B are the points A and B.
LENGTH The length of a line segment determined by A and B is the distance from A to B.
CONGRUENT Two line segments are congruent if they have the same length.
MIDPOINT The midpoint M of segment AB is the point halfway between A and B, such that AM=MB.
BISECTOR The bisector of a line segment is another line, point, or plane that passes through the midpoint of the segment.
ANGLE An angle is the union of two rays that share a common endpoint.
CONGRUENT ANGLE Two angles are congruent if they have the same measure.
ANGLE BISECTOR An angle bisector is a ray or half-plane interior to ABC that divides the angle into two angles with equal measure.
STRAIGHT ANGLE A straight angle is an angle whose sides form a line or whose measure is 180.
ACUTE ANGLE An acute angle is an angle whose measure is between 0 and 90.
RIGHT ANGLE A right angle is an angle whose measure is equal to 90.
OBTUSE ANGLE An obtuse angle is an angle whose measure is between 90 and 180.
COMPLEMENTARY ANGLES Two angles are complementary angles if the sum of their measures is 90.
SUPPLEMENTARY ANGLES Two angles are called supplementary angles if the sum of their measures is 180.
VERTICAL ANGLES Two angles are called vertical angles if their sides form two pairs of opposite rays.
ADJACENT ANGLES Two angles are adjacent if they share a common side and have the same vertex.
PERPENDICULAR LINES Two lines are perpendicular lines if they intersect at right angles.
PERPENDICULAR BISECTOR A perpendicular bisector of a line segment is a line that intersects the segment at a right angle and passes through the midpoint of the segment.
LINEAR PAIR A linear pair of angles is an adjacent pair of angles whose outside rays form a straight angle.
TRIANGLE A triangle is the union of three line segments joining three noncollinear points.
ACUTE TRIANGLE An acute triangle is one in which all angles are acute angles.
OBTUSE TRIANGLE An obtuse triangle is a triangle with one obtuse angle.
RIGHT TRIANGLE A right triangle is a triangle with one right angle. In a right triangle the longest side is called the hypotenuse, and the other two sides are called the legs of the triangle.
EQUILATERAL TRIANGLE An equilateral triangle is a triangle with all angles equal.
SCALENE TRIANGLE A scalene triangle is a triangle with no two sides equal.
ISOSCELES TRIANGLES An isosceles triangle is a triangle with two equal sides. The third side is called the base.
EQUILATERAL TRIANGLE A triangle is called an equilateral triangle if all three sides are equal in length.
CONGRUENT TRIANGLES Two triangles are congruent if all the pairs of corresponding parts are congruent.
PARALLEL LINES Two lines are parallel if they are coplanar and they do not intersect.
SKEW LINES Two lines are skew lines if they are not coplanar.
TRANSVERSAL A transversal is a line that intersects two other coplanar lines.
MEDIAN A median of a triangle is the line segment joining a vertex to the midpoint of the opposite side.
ALTITUDE An altitude of a triangle is a line segment from a vertex perpendicular to the opposite side.
ANGLE BISECTOR OF A TRIANGLE An angle bisector of a triangle is a line segment that extends from a vertex to the side opposite in such a way that it bisects the angle at the vertex.
QUADRILATERAL A quadrilateral is the union of four coplanar segments with each segment intersecting exactly two other segments at the endpoints, and no two segments collinear.
PARALLELOGRAM A parallelogram is a quadrilateral in which both pairs of opposite sides are parallel.
RHOMBUS A rhombus is a parallelogram with four equal sides.
RECTANGLE A rectangle is a parallelogram with four right angles.
SQUARE A square is a rectangle with four equal sides.
TRAPEZOID A trapezoid is a quadrilateral with exactly one pair of opposite sides parallel. The parallel sides are called bases, and the nonparallel sides are the legs. If the legs are equal, the trapezoid is called an isosceles trapezoid.
MEDIAN OF A TRAPEZOID The median of a trapezoid is the line segment that joins the midpoints of the legs of the trapezoid.
POLYGON A polygon is the union of three or more coplanar line segments with each segment intersecting exactly two other segments, one at each endpoint, and with no two intersecting line segments collinear.
PERIMETER The perimeter of a polygon is the sum of the measures of the lengths of the sides.
SIMILAR POLYGONS Two polygons are similar if there is a correspondence between their vertices such that corresponding angles are equal, and corresponding sides are proportional.
SIMILAR TRIANGLES Two triangles are similar if corresponding angles are equal, and corresponding sides are proportional.
CIRCLE A circle is the set of all points in a plane that are a fixed distance from a point called the center of the circle.
RADIUS A radius of a circle is a line segment joining the center of the circle to one of the points on the circle.
DIAMETER A diameter of a circle is a line segment that contains the center of the circle and has its endpoints on the circle.
SECANT A secant is a line that intersects a circle in two points.
TANGENT A tangent to a circle is a line that intersects the circle in exactly one point. The point is called the point of the tangent.
CHORD A chord is a line segment with endpoints on the circle.
ARC An arc of a circle is an unbroken portion of the circle.
SEMICIRCLE An arc of a circle is a semicircle if the endpoints of the arc are on the endpoints of a diameter.
MAJOR ARC A major arc is an arc that is larger than a semicircle. A minor arc is an arc that is smaller than a semicircle.
CENTRAL ANGLE A central angle is an angle whose vertex is at the center of a circle and whose sides are radii of the circle.
CONGRUENT ARCS Two arcs are congruent if they have the same measure and are on the same or congruent circles.
INSCRIBED ANGLE An inscribed angle is an angle whose vertex is on a circle and whose sides intersect the circle in two other points.
INSCRIBED POLYGON A polygon is inscribed in a circle if its vertices lie on the circle.
CIRCUMSCRIBED POLYGON A polygon is circumscribed about a circle if the sides are tangent to the circle.
CONCURRENT LINES Two or more lines are concurrent if they intersect on a single point.
CIRCUMCENTER The circumcenter is the intersection of the perpendicular bisectors of the sides.
INCENTER The incenter is the intersection of the angle bisectors of the triangle.
ORTHOCENTER The orthocenter is the intersection of the lines containing the altitudes of the triangle.
CENTROID The centroid of a triangle is the intersection of the medians of the triangle.