Chương I. §10. Trung điểm của đoạn thẳng
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Unit 10
11/01/2016
MIDPOINT
OF A LINE SEGMENT
Teacher: DO THI DOAN HIEN
Class: 6A1
1
REVIEW
On the ray Ox, draw two line segments OM and
ON so that OM=3cm, ON=6cm.
compute the
length of MN? Compare OM and MN
QUESTION
2
Mr. M, what’s your name?
solution
3cm
O
M
٠
٠
On the ray Ox, draw two
N
x
٠
6cm
0
On the ray Ox, we have OM < ON (3cm<6cm) so that point M is between two
line segments OM and ON
so that OM=3cm, ON=6cm.
points O and N
Calculate the length of
MN? Compare OM and
MN
So we have:
MN = 6
OM + MN = ON
=>
3+
MN = 6 – 3
=>
MN = 3(cm)
So : MN =3 cm
OM = 3cm
OM = MN
⇔
MN =3cm
Point M divides line segment ON into 2 congruent parts.
UNIT 10. MIDPOINT OF A LINE SEGMENT
1. DEFINITION
The point M of line segment AB is the point which is located between A, B and has the equal distance
from A, B.
A midpoint divides a line segment into two congruent segments.
B
A M
Point M is midpoint of line
segment AB
Note: The midpoint of line segment AB is also known as the central point of line segment AB
REMEMBER
A
M
M is midpoint of
line segment AB
B
⇔
oM is between A, B
oM is equidistant from A, B (MA =
MB)
5
APPLY:
M
In each case, is m midpoint of line segment Ab or not, and why?
A
B
A
M
B
A
B
A
M
M
Fig. 1
B
Fig. 3
Fig. 2
Fig. 4
M is not
M is not
MMisisbetween
not
is not
M isMequidistant
Mbetween
is
M is
midpoint of
between A,
but
not
midpoint
of
midpoint
from
but not of
of
andmidpoint
equidistant
line segment
B
equidistant
line segment
line segment
between
A, B
line
from
A,segment
B
AB
from
AB A, B
AB
AB
6
2. How to draw the midpoint of a line
segment?
i) Using straight ruler with measurements
For example:
Draw midpoint K of segment
MN=5cm
M
K
N
1
5
We have: MK = NK = MN = = 2.5(cm)
2
2
7
2. How to draw the midpoint of a line
segment?
ii) Folding paper: Make a midpoint on paper sheet, fold it so that
2 sides overlap to define a midpoint
8
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
