subsets of a line & different kinds of angles
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SUBSETS OF A LINEand
ANGLESMr. Jhon Paul A. Lagumbay
Math Teacher
St. Agnes’ Academy
GOALS:
a. Illustrates subsets of a line
b. Use some postulates and theorems that relate points, lines, and planes
c. Distinguish between segments, rays and lines
d. Find the distance between two points on a number line
e. Find the coordinate of the midpoint of a segment
f. Identify opposite rays and angles
g. Measure, classify and identify types of angles.
SUBSETS OF A LINE
A B
Segment AB, denoted by or is the union of points A, B and all the points between them. A and B are called the endpoints of the segment.
Definition of a Segment
A segment is a subset of a line.
The length of the segment is the distance between its endpoints.
A BP
Point P is said to be between A and B if and only if A, P, and B are distinct points of the same line and .
Definition of Between
A BP
Ray AP, denoted by is the union of (a) and (b) all points B such that P is between A and B .
Definition of a Ray
A ray is another subset of a line.
A ray starts at one point of a line and goes on indefinitely in one direction.
Ray AP, denoted by is the union of (a) and (b) all points B such that P is between A and B .
Definition of a Ray
and are described as opposite rays if and only if they are subsets of the same line and have a common endpoint.
A BP
Relationships Among Points, Lines and Planes
A postulate is a statement which is accepted as true without proof.
A statement that needs to be proven is called a theorem.
A corollary is a theorem whose justification follows from another theorem.
A line contains at least two distinct points. A plane contains at least three noncollinear points. Space contains at least four noncoplanar points.
Postulate 1
If two distinct points are given, then a unique line contains them.
Postulate 2 – Line Postulate
A Bl
The points A and B determine exactly one line l. This means that there is one and only one line l that contains points A and B.
If two distinct lines intersect, then they intersect at exactly one point.
Theorem 1
Lines l and m intersect at K.
m
l
K
Three collinear points are contained in at least one plane and three noncollinear points are contained in exactly one plane.
Postulate 3
The noncollinear points A, B, and C are contained in exactly one plane P whereas the collinear points D, E, and F in at least one plane.
If two distinct planes intersect, then their intersection is a line.
Postulate 4
S
T
l
If two points are in a plane, then the line that contains those points lies entirely in the plane.
Postulate 5
A Bl
E
A line that lies in a plane divides the plane into two subsets, each of which is called a half-plane. The dividing line is called the edge.
If a line not contained in a plane intersects the plane, then the intersection contains only one point.
Theorem 2
If line l and plane E intersect two points A and B, then line l lies in plane E by Postulate 5. But this could not be since line l is not contained in plane E.
AB
E
l
If two distinct lines intersect, then they lie in exactly one plane.
Theorem 3
m
l
K
If there is a line and a point not in the line, then there is exactly one plane that contains them.
Theorem 4
A Bl
ER
Given any two points there is a unique distance between them.
Postulate 6
A
0-4 5
B
There is one-to-one correspondence between the points of a line and the set of real numbers such that the distance between two distinct points of the line is the absolute value of the difference of their coordinates.
Postulate 7 – The Ruler Postulate
A
0 3 10
B
S T
Distance ST
The length or measure , ST,
of a segment, , is the
distance between S and T.
0 5
A B
3
C D
8
Two segments are congruent if and only if they have equal
measures. if and only if .
A point of a segment is its midpoint if and only if divides the
segment into two congruent segments. M is the midpoint of if
and only if .
S TM
On a ray there is exactly one point that is at a given distance from the endpoint of the ray.
Theorem 5
Each segment has exactly one midpoint.
Corollary 1
X YM
R
T
kZ
Any line, segment, ray, or plane that intersects a segment at its midpoint is called a bisector of the segment.If M is the midpoint of , then the line , plane , and all bisect .
If M is the midpoint of a segment AB, denoted as , then
and
Theorem 6 – Midpoint Theorem
A BM
EXAMPLE:
I
0-3 3
J
6
H
A
F
D
E
GC
B
GIVEN: , , , , , and
a. What is the midpoint of ?
b. Name four bisectors of .
c. What is the midpoint of ?
d. What segment is congruent to ?
e. Is B between I
and D?
Angles
A figure is an angle if and only if it is the union of two noncollinear rays with a common endpoint.
Definition
X
ZY
noncollinear rays - SIDES
common endpoint - VERTEX
SIDES: ,
VERTEX:ANGLE: or
B
Q
A
R
C
PZ
1interior
exterior
An angle in a plane separates it into three sets of points:a. the points in the interior
of the angle;b. the points in the exterior
of the angle; andc. the points on the angle
itself.
Thus, R is an interior point, P is an exterior point and Q is a point on the angle.
An angle can also be named by a number or by its vertex.
Two coplanar angles are adjacent if and only if they satisfy three conditions: (1) they have a common vertex , (2) they have a common side , and (3) they have no common interior points.
Definition
EXAMPLE:
Use the figure to name the following:
a. An angle named by one letter.
b. The sides of
c. and with lettersd. An angle adjacent to
YZ
X
C
B A
12
3
Classifying Angles According to Measures
AngleName of the Angle
Measure of the Angles
Classification
Less than Acute Angle
Equal to Right Angle
Greater than but less than
Obtuse Angle
2
1
3
is an acute angle if and only if the measure of is greater than 0 but less than 90. In symbol,
is a right angle if and only if the measure of is 90. In symbol,
is an obtuse angle if and only if the measure of is greater than 90 but less than 180. In symbol,
Definition
Given any angle, there is a unique real number between 0 and 180 known as its degree measure.
Postulate 8 – Angle Measurement Postulate
In a half-plane with edge any point S between A and B, there exists a one-to-one correspondence between the rays that originate at S in that half-plane and the real numbers between 0 and 180
To measure an angle formed by two of these rays, find the absolute value of the difference of the corresponding real numbers.
Postulate 9 – The Protractor Postulate
In a half-plane, through the endpoint of ray lying in the edge of the half-plane, there is exactly one other ray such that the angle formed by two rays has a given measure between 0 and 180.
Postulate 10 – The Angle Construction Postulate
Two angles are congruent if and only if they have equal measures. In symbols, if and only if
Definition
All right angles are congruent.
Theorem 7
GIVEN: three coplanar rays, , and , is between and if and only if
A
O B
T
A ray is a bisector of an angle if and only if it divides the angle into two congruent angles, thus angles of equal measure.
Definition
If is a bisector of , then
and
Theorem 8 – Angle Bisector Theorem
If T is in the interior of , then
Postulate 11 – Angle Addition Postulate
A
O B
T
ILLUSTRATE & ANSWER THE FOLLOWING:
1. If and , what can you conclude about ?
2. If and , what can you conclude about ?
That in all things, God may be Glorified!!!
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