# 10th grade geometry A Chapter 1

Adjacent Angles Two coplanar angles that have a common side and a common vertex but no common interior points.
Axiom or Postulate An accepted statement of fact – one that has not been proven but is still considered true.
Collinear Points that lie on the same line.
Complementary Angles Two angles whose sum of their measures is 90 degrees.
Congruent Angles Angles that have the same measure.
Congruent Segments Segments that have the same measure.
Conjecture A conclusion reached by using inductive reasoning.
Coplanar Points or objects that lie on the same plane.
Counterexample A particular instance, situation or thing that makes the statement false.
Foundation Drawing An illustration showing the base of a structure and the height of each part.
Inductive Reasoning A type of logical thinking that reaches conclusions based on a pattern of specific examples or past events.
Isometric Drawing An illustration of a three-dimensional object showing a corner view of a figure.
Midpoint The point that divides a segment into two congruent segments.
Net A two-dimensional pattern that you can fold to form a three-dimensional figure.
Orthographic Drawing An illustration of a three-dimensional object showing the top, right and front views.
Parallel Lines Lines which lie in the same plane and do not intersect. They have the same "direction".
Parallel Planes Planes that do not interesect.
Skew Lines Lines that do not lie in the same plane (and do not intersect). They have different "directions".
Straight Angle An angle whose measure is 180 degrees.
Supplementary Angles Two angles whose sum of their measures is 180 degrees.
Vertical Angles Two angles with sides that are opposite rays.
|a – b| The formula for the distance between points on a number line.
{(x1+x2)/2, (x1+x2)/2} The formula for the midpoint of a line segment on a plane.
A = ?r2 The formula for the area of a circle.
C = 2?r = ?d The formula for the circumference of a circle.
A = BH = LW The formula for the area of a rectangle.
P = 2l + 2w = 2(l + w) The formula for the perimeter of a rectangle.
d = sq root of {(x2 – x1)^2 + (y2 – y1)^2} The formula for the distance between points on a plane.
Perpendicular bisector A line, segment, or ray that divides a segment into two congruent segments and lies at a 90 degree angle.
Angle bisector A ray that divides an angle into two congruent angles.