Geometry Vocabulary 7-1By: Hilary Clinger & Alex Shipherd

Point

• An exact location in a space• Represented by a dot• Named by a capital letter

A

Line

• A collection of points along a straight path extending forever in opposite directions

• Draw a line with arrows on both ends• Named by any to points on the line in either

orderK JL

Line Segment

• Part of a line with two endpoints, it has both a beginning and an end

• It can be measured, using a ruler• Drawn as a line with no arrows• Named by the two endpoints, in either order

P O

Endpoint

• Where a ray begins

Endpoint

Ray

• Part of a line that extends forever in only one direction

• Where it begins is called the endpoint• Drawn as a line with only on arrow• Named by the endpoint and any other point

on the ray, endpoint always comes first

Plane

• A flat surface that extends in all directions forever

• Anything than can be drawn in a plane is called a plane figure

• Named by three points in the plane

Intersecting Lines

• Intersect or meet at one point

DC

BA

F

Parallel Lines

• Do not intersect anywhere, where they remain

Perpendicular Lines

• A special kind of intersecting lines form right angles at the point of intersection.

Concurrent Lines

• Intersect everywhere one line lays on top of the other lines

Angle

• An angle is formed by two rays that have a common endpoint called the vertex

• The rays are the sides of the angle• Drawn with two rays

Angles (continued)

• Named by three points one on each ray and the vertex is always in the middle

• Or named by the vertex• Or named by a number• We can measure an angle in degrees using a

protractor

Acute Angle• Measures between

0° and 90°

Right Angle

Obtuse Angle Straight Angle

• Measures exactly 90°

• Measures between 90° and 108°

• Measures exactly 180°

Protractor

• A protractor is used to measure angles• You can draw angles by using protractors

How to use a Protractor:Step 1: Center the protractor on the vertex of the angle

Step 2: Align the 0° mark on one side of the angle

Step 3: Read the measure where the other side passes through the protractor

SupplementaryAngles

• Two angles whose sum of their measures is equal to 90° are complementary angles

ComplementaryAngles

• Two angles whose sum of their measures is equal to 180° are supplementary angles

1

2

m 1+m 2= 90° m 3+m 4= 180°

3 4

Adjacent Angles Vertical Angles

• Share the common vertex and a common side

• Share only the common vertex. The measures of the vertical angles are equal

C

DE

F

G120°

120°60°60°

Think:m EDG = m CGFm CGE = m FGD

J

A

L

M

Think: JAL is adjacent to LAM

Transversal

• Two pairs of parallel lines are both intersected by a third line, several pairs of congruent angles are formed. At each point of intersection two pairs of vertical angles are formed.

1 2

3

45 6

8 7

Corresponding Angles

• Are congruent

1 2

3

45 6

8 7

m 1= m 5m 2= m 6m 3= m 7m 4= m 8

Alternate Interior Angles

• The measure of the angles on opposite sides of the transversal both inside and outside the parallel lines are equal.

Alternate Exterior Angles

• The measure of the angles on opposite sides of the transversal both inside and outside the parallel lines are equal.

1 2

3

45 6

8 7

1 2

3

45 6

8 7

Triangle

• Polygon with 3 sides, angles, and vertices. • Different sizes and shapes• Classified according to the length of their sides

or according to the measure of their angles

Acute Triangle

• Three acute angles

Right Triangle

• One 90° angle• Two acute angles (less than 90°)

Obtuse Triangle

• One obtuse angle• Two acute angles

Scalene Triangle

• No congruent sides • No congruent angles

Isosceles Triangle

• Two congruent sides• Two congruent angles

Equilateral Triangle

• Three congruent sides• Three congruent angles

Reflection

• A flip

Line of Symmetry

• When you can fold a shape and have it match perfectly with itself

A heart has one line of symmetry. A square has four.

Dilation

• To dilate a polygon, multiply the coordinates of each vertex by the scale factor and connect the vertices.

Image

• The shape after it has been reflected

Image

Rotation

• When you turn a shape

Transformation

• Moving a shape but not changing it

Translation

• When you slide a shape

The rest of the vocabulary is on our wikis.Geometry List Vocabulary 7-1

By: Hilary Clinger and Alex Shipherd