Geometry Terms from Chapter 5 New terms from chapter 5 and a few old terms students are having trouble with. Tools A B Linear Pair Two adjacent angles whose noncommon sides are opposite rays. Linear Pair Postulate If two angles form a linear pair, then they are supplementary. Vertical Angles Theorem Vertical angles are congruent. Vertical Angles Two angles whose sides form two pairs of opposite rays. Perpendicular Lines that meet to form a right angle. Angle Bisector A ray that cuts an angle into two congruent angles. Segment Bisector Goes through the midpoint of a segment. Midpoint The point that cuts a segment into two congruent segments. A Theorem about Perpendicular Lines. Perpendicular lines form four right angles. A Theorem about Right Angles. All right angles are congruent. Corollary A theorem that follows easily from a previously proved theorem. Equilateral Triangle A triangle with three congruent sides. Equiangular Triangle A triangle with three congruent angles. Scalene Triangle A triangle with no congruent sides. Isosceles Triangle A triangle with at least two congruent sides. Altitude A segment from a vertex of a triangle that is perpendicular to the opposite side or to the line containing the opposite side. Centroid The point where the medians of a triangle intersect. Centroid It is two-thirds of the distance from each vertex to the midpoint of the opposite side. Circumcenter The point where the perpendicular bisectors of a triangle intersect. Circumcenter It is equidistant from the three vertices of the triangle. Circumcenter It is the center of the circumscribed circle. Concurrent Two or more lines or segments that intersect in a single point. Incenter The point where the three angle bisectors intersect. Incenter It is equidistant from the three sides of the triangle. Incenter It is the center of the inscribed circle. Median A segment whose endpoints are a vertex of the triangle and the midpoint of the opposite side. Midsegment A segment that connects the midpoints of two sides of a triangle. Orthocenter The point where the altitudes of a triangle intersect. Perpendicular Bisector A line that is perpendicular to a side of a triangle at its midpoint.