acute angle		a flat surface that has no thickness
angle bisector		a ray that divides an angle into two congruent coplanar angles
collinear points		distance and direction from the origin of a number line
congruent angles		a 180 degree angle
congruent segments		an angle between 90 and 180 degrees
conjecture		a 90 degree angle
coordinate		angle with the same measure
coplanar		part of a line consisting of two endpoints and all points between them
counterexample		noncoplanar lines
inductive reasoning		coplanar lines that do not intersect
obtuse angle		points that lie on the same line
parallel lines		an accepted statement of fact
parallel planes		a line, segment, or ray that is perpindicular to the segment at its midpoint
perpindicular bisector		part of a line consisting of one endpoint and all the points of the line on one side of the endpoint
perpindicular lines		reasoning based on patterns one observes
plane		points (or lines) that are in the same plane
postulate		a conclusion reached using inductive reasoning
ray		planes that do not intersect
right angle		a positive angle less than 90 degrees
segment		two segments with the same length
skew lines		two lines that intersect to form right angles
straight angle		an example for which the conjecture is incorrect