Introduction to Geometry &

Measurements

Roxanne Joie V. Deang

BSE Math IV

POINTS, LINES, & PLANES

POINTS

Point

basic element in geometry represented by a dot (.)

an idea that shows an exact location in space

no dimension; no length; no width and no thickness

named using a capital letter

LINES

Line

set of infinite points extended endlessly or indefinitely in two directions

represented by a stretch string, edge of a table, etc.

it has one dimension which is the length named by one small letter or two capital

letters

Name this line!

L O V E

PLANES

Plane

set of infinite points extended in four directions

it has two dimensions – length and width represented by any flat surface named by at least three points of the plane

provided that the points must not lie along the same line

Name this

plane!

JV

A

RK

N

D

M

L

RAYS & ANGLES

RAYS

Ray

a part of a line that extends indefinitely in one direction

named by writing the endpoint first and then another point on the ray

R O X

ANGLES

Angle

formed by two rays with a common endpoint the common endpoint is called the

vertex the two rays are called the sides of the

angle

Angle

when naming an angle, the letter designating the vertex should always stand between two other letters.

an angle can also be named by using a single letter designating the vertex

A

B

C

Angle

angles are measured in units called degrees (o)

a protractor is used to measure angles

KINDS OF ANGLES ACCORDING TO MEASUREMENT

RIGHT ANGLE

Right Angle

an angle whose measure is 90o

a small square is usually placed to indicate a right angle

Right Angle

E

D F

ACUTE ANGLE

an angle whose measure is greater than 0o and less than 90o

Acute Angle

Acute Angle

H

G I

OBTUSE ANGLE

Obtuse Angle

an angle whose measure is greater than 90o but less than 180o

Obtuse Angle

K

J L

Try this!

1.) 2

Use the figure to answer each questions below.

What kind of angle is each? Write A for Acute, R for Right and O for Obtuse.

12 3

4A

B CD

E

2.) 4

3.) 1 + 2

4.) 2 + 3

5.) 2 + 3 + 4

6.) 1 + 2 + 3

A1

A2

R3

O4

O5

O6