Chương I. §10. Trung điểm của đoạn thẳng

Unit 10
MIDPOINT
OF A LINE SEGMENT
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Teacher: DO THI DOAN HIEN
Class: 6A1
11/01/2016
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
REVIEW
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QUESTION
٠
٠
M
N
3cm
6cm
On the ray Ox, we have OM < ON (3cm<6cm) so that point M is between two points O and N
So we have: OM + MN = ON 3 + MN = 6 => MN = 6 – 3 => MN = 3(cm)
So : MN =3 cm
OM = MN
Point M divides line segment ON into 2 congruent parts.
On the ray Ox, draw two line segments OM and ON so that OM=3cm, ON=6cm. Calculate the length of MN? Compare OM and MN
OM = 3cm MN =3cm
solution
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.
Note: The midpoint of line segment AB is also known as the central point of line segment AB
UNIT 10. MIDPOINT OF A LINE SEGMENT
1. DEFINITION
A
B
Point M is midpoint of line segment AB
REMEMBER
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M is midpoint of
line segment AB
M is between A, B
M is equidistant from A, B (MA = MB)
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M is not between A, B
M is between but not equidistant from A, B
M is equidistant from but not between A, B
M is between and equidistant from A, B
M is not midpoint of line segment AB
APPLY: In each case, is m midpoint of line segment Ab or not, and why?
M is not midpoint of line segment AB
M is not midpoint of line segment AB
M is midpoint of line segment AB
2. How to draw the midpoint of a line segment?
i) Using straight ruler with measurements
For example:
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M
N
K
Draw midpoint K of segment MN=5cm
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
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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
A
B
M
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iii) Folding rope: Using a rope to divide a straight wooden stick into two equal parts
2. How to draw the midpoint of a line segment?
?
?
?
?
Using a rope to measure wooden stick, and then fold it so that two end points overlap each other, using folded rope to identify midpoint of wooden stick.
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B
M
A
vi) Using compass
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Midpoint geometry in real life
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Exercise 63 (Work book Page 126): Select correct answers in the following conclusions
A
B
C
D
IA = IB
AI + IB = AB
AI + IB = AB and IA = IB
3. DO EXERCISES
RIGHT
RIGHT
WRONG
WRONG
‹#›
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MN = 40 cm
Bonus: Let H is midpoint of line segment MN, and MH=20 cm.
Calculate the length of line segment MN?
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Consolidating Lesson
Remind : when point M is called a midpoint
of line segment AB?
M is midpoint of
line segment AB
M is between A, B
M is equidistant from A, B (MA = MB)
Do homework: 64, 65 workbook p. 126
Thanks for your atention
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