Geometry Terms

Front 1

Point

Back 1

A representation of a position with zero size.

Front 2

Line

Back 2

An set of infinitely connected points. It extends infinitely into two directions. It has infinite length and zero width & hight.

Front 3

Collinear Points

Back 3

Points that all lie on the same line.

Front 4

Noncollinear Points

Back 4

Points that don't all lie on the same line.

Front 5

Plane

Back 5

An infinite set of points forming a connected flat surface extending infinitely far in all directions. A plane has infinite length, infinite width, and zero height (or thickness). It is usually represented in drawings by a four-sided figure.

Front 6

A line contains at least two points.

Back 6

Postulate 1

Front 7

A plane contains at least three noncollinear points.

Back 7

Postulate 2

Front 8

Through any two points, there is exactly one line.

Back 8

Postulate 3

Front 9

Through any three noncollinear points, there is exactly one
plane.

Back 9

Postulate 4

Front 10

f two points lie in a plane, then the line joining them lies in that plane

Back 10

Postulate 5

Front 11

If two planes intersect, then their intersection is a line.

Back 11

Postulate 6

Front 12

If two lines intersect, then they intersect in exactly one point.

Back 12

Theorem 1

Front 13

If a point lies outside a line, then exactly one plane contains
both the line and the point.

Back 13

Theorem 2

Front 14

If two lines intersect, then exactly one plane contains both lines.

Back 14

Theorem 3

Front 15

Line Segment

Back 15

a connected piece of a line. It has two endpoints and is named by its endpoints.

Front 16

Each point on a line can be paired with exactly one real number called its coordinate. The distance between two points is the positive difference of their coordinates.

Back 16

Postulate 7

Front 17

If B lies between A and C on a line, then AB + BC = AC.

Back 17

Postulate 8 (Segment Addition Postulate)

Front 18

A lies between C and T. Find CT if CA = 5 and AT = 8.

Back 18

Because A lies between C and T, Postulate 8 tells you
CA +AT = CT
5 + 8 = 13
CT = 13

Front 19

Midpoint

Back 19

the halfway point, or the point equidis- tant from the endpoints.

Front 20

A line segment has exactly one midpoint.

Back 20

Theorem 4

Front 21

How do you find the midpoint of a line segment?

Back 21

Subtract the larger endpoint value of the line segment from the lesser endpoint value and divide it by 2. You can also add the endpoint values and divide the sum by 2.

Front 22

Ray

Back 22

a piece of a line, except that it has only one endpoint and continues forever in one direction. It could be thought of as a half-line with an endpoint.

Front 23

Angle

Back 23

Two rays that have the same endpoint form an angle. That endpoint is called the vertex, and the rays are called the sides of the angle. In geome- try, an angle is measured in degrees from 0° to 180°.

Front 24

The positive difference between two numbers representing two different rays is the measure of the
angle whose sides are the two rays.

Back 24

Postulate 9

Front 25

Postulate 9

Back 25

The positive difference between two numbers representing two different rays is the measure of the
angle whose sides are the two rays.

Front 26

If line OB lies between OA and OC, m ∠AOB + m ∠BOC = m ∠AOC.

Back 26

Postulate 10 (Angle Addition Postulate)

Front 27

Postulate 10 (Angle Addition Postulate)

Back 27

If line OB lies between OA and OC, m ∠AOB + m ∠BOC = m ∠AOC.

Front 28

Angle Bisector

Back 28

An angle bisector is a ray that divides an angle into two equal angles.

Front 29

Theorem 5

Back 29

An angle that is not a straight angle has exactly one bisector.

Front 30

Right Angle

Back 30

A right angle has a measure of 90°. The little box in the interior of an angle designates the fact that a right angle is formed.

Front 31

Theorem 6

Back 31

All right angles are equal.

Front 32

Adjacent Angles

Back 32

Adjacent angles are any two angles that share a common side separating the two angles and that share a common vertex.

Front 33

Vertical Angles

Back 33

Vertical angles are formed when two lines intersect and form four angles. Any two of these angles that are not adjacent angles are called vertical angles.

Front 34

Theorem 7

Back 34

Vertical Angles are equal in measure.

Front 35

Complimentary Angles

Back 35

Complementary angles are any two angles whose sum is 90°.

Front 36

Theorem 8

Back 36

If two angles are complementary to the same angle, or to equal angles, then they are equal to each other.

Front 37

Supplementary Angles

Back 37

Supplementary angles are two angles whose sum is 180°.

Front 38

Theorem 9

Back 38

If two adjacent angles have their noncommon sides lying on a line, then they are supplementary angles.

Front 39

Theorem 10

Back 39

If two angles are supplementary to the same angle, or to equal
angles, then they are equal to each other.