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An angle with a measure between 0 degrees and 90 degrees. acute angle
Two angles that share a common vertex and side, but have no common interior points. adjacent angles
A segment that originates at the vertex of a triangle and makes a right angles with the line that contains the opposite side. altitude
A segment that divides an angle of a triangle into two equal parts. angle bisector
Two true conditional statements that are converses of each other. biconditional
Point of intersection of the medians. circumcenter
Two angles whose sum of their measures is 90 degrees. complementary angles
Three or more lines that intersect at one point. concurrent lines
Two geometric figures that are the same size and shape. congruent figures
An unproved statement that seems to be true. conjecture
The statement formed by switching the hypothesis and conclusion of a conditional statement. converse
The statement formed when you negate the hypothesis and conclusion of the converse of a conditional statement. contrapositive
An example that shows a conjecture is false. counterexample
A polygon with 10 sides. decagon
Reasoning logically from accepted facts. deductive reasoning
A polygon with 12 sides. dodecagon
A triangle with 3 congruent angles. equiangular triangle
A triangle with 3 congruent sides. equilateral triangle
A polygon with 7 sides. heptagon
A polygon with 6 sides. hexagon
Point of intersection of the angle bisectors. incenter
Reasoning that includes making conclusion based on observations. inductive reasoning
The statement formed when you negate the hypothesis and conclusion of a conditional statement. inverse
A triangle with at least 2 congruent sides. isosceles triangle
Two adjacent angles whose non-common sides are opposite rays. linear pair
A segment that connects a vertex of a triangle to the midpoint of the opposite side. median
A point that divides a segment into 2 congruent segments. midpoint
A polygon with 9 sides. nonagon
An angle whose measure is between 90 degrees and 180 degrees. obtuse angle
A polygon with 8 sides. octagon
Point of intersection of the altitudes. orthocenter
Two coplanar lines that do not intersect. parallel lines
A polygon with 5 sides. pentagon
A segment that intersects the side of a triangle at its midpoint and makes a right angle. perpendicular bisector
Lines that intersect to form a right angle. perpendicular lines
A statement that is accepted as true without proof. postulate
A polygon with 4 sides. quadrilateral
A set of points extending infinitely in one direction. ray
A polygon that is both equiangular and equilateral. regular polygon
An angle with the measure of 90 degrees. right angle
A triangle with no congruent sides. scalene triangle
A part of a line with two endpoints. segment
Two non-coplanar lines that do not intersect. skew lines
The set of all points. space
An angle with the measure of 180 degrees. straight angle
Two angles whose sum measures 180 degrees. supplementary angles
A statement that must be proved to be true. theorem
A line that intersects two or more coplanar lines at different points. transversal
Two angles whose sides form two sets of opposite rays. vertical angles
Created by: kwillcockson