Download Geometry unit 1 vocabulary

Vocabulary Definitions Unit 1
Point: Indicates a location and has no size. You will name a point by using a capital
letter.
Point A
Line: Extends in two opposite directions without ending. It has no thickness. A line
contains an infinite number of points. We name a line with two points on the line or by
a single lowercase letter.
⃡
Line 𝑙 or 𝐴𝐵
Plane: is a flat surface that extends without end and has no thickness. A plane contains
an infinite number of lines. A plane is name by a capital letter or by at least 3 points
within in the plane that are NOT on the same line.
Plane P or Plane ABC
Space: the set of all points.
Collinear points: points that lie on the same line.
Points D, E and F are collinear.
Coplanar points: points that lie in the same plane. (You can also have other coplanar
figures)
Points A, B and C are coplanar in Plane P.
Segment: a part of a line that consists of two endpoints and all the points in between
them. You name a segment by its two endpoints.
Segment ̅̅̅̅
𝐴𝐵 or ̅̅̅̅
𝐵𝐴
Ray: is part of the line that consists of only one endpoint and all the points on one side
of the line. You name a ray by its endpoint and one point on the ray. The order of the
points indicates the ray’s direction.
Ray 𝐴𝐵
Opposite Rays: Two rays that share the same endpoint and form a line.
𝐸𝐷 𝑎𝑛𝑑 𝐸𝐹 are opposite rays.
Congruent Segments: segments that have equal measure.
Midpoint of a Segment: The point on a segment that divides it into two congruent
segments.
Segment Bisector: The ray, segment, line or plane that intersects a segment at its
midpoint.
Segment Addition Postulate: If points A, B and C are collinear and B is between A and C,
then AB + BC = AC.
Ratio: A comparison of two quantities using division.
Partition: to divide into parts.
Angle: Formed by two rays or segments with a common endpoint. The rays are the sides
of the angle and the vertex is the common endpoint.
∠𝐵𝐴𝐶, ∠𝐶𝐴𝐵,∠𝐴 or ∠1
Acute Angle: an angle whose measure is between 0 and 90 degrees.
Right Angle: an angle whose measure is exactly 90 degrees.
Obtuse Angle: an angle whose measure is between 90 and 180 degrees.
Straight Angle: an angle whose measure is exactly 180 degrees.
Adjacent Angle: two angles is a plane that have a common vertex and common side but
no common interior points.
Linear Pair: A pair of angles who non-common sides are opposite rays. They form a
straight angle, so therefore, they are supplementary.
Angle Addition Postulate: The measure of the smaller angles will sum to the whole
angle. 𝑚∠𝐴𝑂𝐵 + 𝑚∠𝐵𝑂𝐶 = 𝑚∠𝐴𝑂𝐶.
Vertical Angles: two angles whose sides form opposite rays. Their measures are
congruent.
Complementary Angles: two angles whose measures sum to 90 degrees.
Supplementary Angles: two angles whose measures sum to 180 degrees.
Angle Bisector: a ray that divides an angle into two congruent angles.
Congruent Angles: angles that have the same measure
Conditional: an if-then statement. It has 2 parts, they hypothesis which comes after the
if and the conclusion which is after the then. “If p, then q.”
Converse: switch the hypothesis and conclusion of the conditional statement. “If q, then
p.”
Inverse: Negate the conditional statement. “if not p, then not q.”
Contrapositive: Negate the converse statement. “If not q, then not p.”
Truth Value: determines if a conditional is true or false.
Hypothesis true and conlusion true…………….statement is true.
Hypothesis true and conclusion false………….statement is false.
Counterexample: an example that proves a statement false.
Parallel Lines: coplanar lines that never intersect.
a ll b
Perpendicular Lines: coplanar lines that intersect and form a right angle.
Skew Lines: noncoplanar lines that never intersect and are not parallel.
⃡𝐴𝐵 and ⃡𝐷𝐸 are skew.
Parallel Planes: two planes that never intersect.
Perpendicular Planes: two planes that intersect at a right angle.
Transversal: a coplanar line that intersects two or more lines.
Corresponding Angles: angles that lie in the same position (corresponding position)
relative to the transversal.
Corresponding angles are congruent, IF lines are parallel.
Alternate Interior Angles: nonadjacent interior angles that are on opposite sides of the
transversal.
Alternate interior angles are congruent, IF lines are parallel.
Alternate Exterior Angles: nonadjacent exterior angles that are on opposite sides of the
transversal.
Alternate Exterior angle are congruent, IF lines are parallel.
Same-Side Interior Angles: Interior angles on the same side of the transversal.
Same-Side interior angles are supplementary, IF lines are parallel.
Same-Side Exterior Angles: Exterior angles on the same side of the transversal.
Same-Side exterior angles are supplementary, if lines are parallel.
Angles 1 and 8 are Same-Side Exterior angles.
Angles 2 and 7 are Same-Side Exterior angles.