Download Chapter 1 Vocabulary

Geometry Vocabulary
Vocabulary Term
1. Point
2. Line
3. Ray
4. Line Segment
Example
Definition/Description
One of the basic undefined terms of
geometry. Traditionally thought of as
having no length, width, or thickness,
and often a dot is used to represent it.
We usually represent a point with a
dot on paper, but the dot we make
has some dimension, while a true
point has no dimension.
One of the basic undefined terms of
geometry. Traditionally thought of as
a set of points that has no thickness
but its length goes on forever in two
opposite directions. AB denotes a
line that passes through point A and
B.
Has no beginning or end.
Cannot measure its length.
A ray begins at a point and goes on
forever in one direction.
Must name stating the endpoint first.
The part of a line between two points
on the line. AB denotes a line
segment between the points A and B.
Can be measured.
5. Collinear
Points that are on the same line are
collinear
6. Plane
One of the basic undefined terms of
geometry. Traditionally thought of as
going on forever in all directions (in
two-dimensions) and is flat (i.e., it has
no thickness).
7. Coplanar
Points that lie on the same plane are
coplanar
8. Space
A boundless, three-dimensional set of
all points. Contains lines and planes.
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9. Congruent
Having the same size, shape and
measure. Two figures are congruent
if all of their corresponding measures
are equal.
10. Midpoint
Divides a segment into two equal
parts.
11. Bisector
A bisector divides a segment or angle
into two equal parts.
12. Degree
1/360 of a turn around a circle
13. Angle
Angles are created by two distinct
rays that share a common endpoint
(also known as a vertex). ABC or B
denote angles with vertex B.
Naming Angles:
14. Interior/
Exterior angles
An angle inside (interior) or outside
(exterior) of a figure/shape.
15. Remote Interior
angles of a
Triangle
The two angles non-adjacent to the
exterior angle.
16. Right angle
An angle whose measure is exactly 90
degrees.
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17. Acute angle
An angle whose measure is between
0 and 90 degrees.
18. Obtuse angle
An angle whose measure is greater
than 90 but less than 180 degrees.
19. Opposite Rays/
Straight Angle
Rays that share a common endpoint
and extend infinitely in opposite
directions.
20. Adjacent
angles
Angles in the same plane that have a
common vertex and a common side,
but no common interior points.
21. Vertical angles
Two nonadjacent angles formed by
two intersecting lines or segments.
Also called opposite angles.
22. Linear pair
A pair of adjacent angles with
noncommon sides that are opposite
rays.
23. Complementary angles
Two angles with measures that have
a sum of 90 degrees.
24. Supplementary angles
Two angles with measures that have
a sum of 180 degrees.
25. Perpendicular
Lines, segments, or rays that intersect
to form right angles.
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26. Parallel
Lines, segments, or rays that lie in the
same plane but never intersect.
27. Skew Lines
Two lines that do not lie in the same
plane (therefore, they cannot be
parallel or intersect).
28. Angles formed
by parallel lines
being cut by a
transversal
The angles have special names
identifying their positions with respect
to the parallel lines and transversal.
They are corresponding angles,
alternate exterior angles, alternate
interior angles, same side interior
angles, or same side exterior angles.
An angle is congruent to its matched
angle.
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Same side interior: angles 3 & 6 and
angles 4 & 5
Same side exterior: angles 1 & 8 and
angles 2 & 7
29. Polygon
A closed figure whose sides are all
segments.
30. Regular
polygon
A convex polygon in which all the
sides are congruent (equilateral) and
all the angles are congruent
(equiangular).
31. Similar Figures
Figures that have the same shape but
not necessarily the same size.
32. Correspon-ding
Sides
Sides that have the same relative
positions in geometric figures.
33. Correspon-ding
Angles
Angles that have the same relative
positions in geometric figures.
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34. Transforma-tion
The mapping, or movement, of all the
points of a figure in a plane
according to a common operation.
35. Translation
A transformation that "slides" each
point of a figure the same distance in
the same direction
36. Dilation
Transformation that changes the size
of a figure, but not the shape.
37. Scale Factor
The ratio of any two corresponding
lengths of the sides of two similar
figures.
38. Reflection
A transformation that "flips" a figure
over a line of reflection.
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39. Reflection Line
A line that is the perpendicular
bisector of the segment with
endpoints at a pre-image point and
the image of that point after a
reflection.
40. Rotation
A transformation that turns a figure
about a fixed point through a given
angle and a given direction.
41. Perimeter
The sum of the length of the sides of a
polygon.
42. Circumference
The distance around a circle.
43. Area
The number of square units needed
to cover a surface.
The amount of space a figure takes
up.
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44. Surface area
The sum of the areas of each face of
a solid.
45. Volume
The measure of the amount of space
the solid encloses.
46. Altitude
A line drawn from the vertex of a
triangle perpendicular of the
opposite side.
47. Median
48. Perpendicular
Bisector
Every triangle has 3 altitudes – one
drawn from each vertex.
A line drawn from the vertex of a
triangle to the midpoint of the
opposite side.
Every triangle has 3 medians – one
drawn from each vertex.
A perpendicular line that passes
through the midpoint of each side of
a triangle.
Every triangle has 3 perpendicular
bisectors – one drawn through each
side.
49. Angle Bisector
Line drawn from the vertex of a
triangle so that it bisects the angle
from which it is drawn.
Every triangle has 3 angle bisectors –
one drawn from each vertex.
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50. Centroid
The point of concurrency of the
medians of a triangle.
51. Circumcenter
The point of concurrency of the
perpendicular bisectors of the sides of
a triangle.
52. Incenter
The point of concurrency of the
bisectors of the angles of a triangle.
53. Orthocenter
The point of concurrency of the
altitudes of a triangle.
54. Conditional
Statement
A statement written in if-then form.
55. Hypothesis
The “if” portion of a conditional
statement.
56. Conclusion
The “then” portion of a conditional
statement.
57. Converse
The reverse of a conditional
statement (reverse the hypothesis
and the conclusion).
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58.
59.
60.
61.
62.
63.
64.
65.
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