Chương I. §10. Trung điểm của đoạn thẳng

Unit 10 11/01/2016 MIDPOINT OF A LINE SEGMENT Teacher: DO THI DOAN HIEN Class: 6A1 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 Mr M, what’s your name? solution 3cm O M ٠ ٠ On the ray Ox, draw two N x ٠ 6cm On the ray Ox, we have OM < ON (3cm 3+ MN = – => MN = 3(cm) So : MN =3 cm OM = 3cm OM = MN ⇔ MN =3cm Point M divides line segment ON into congruent parts UNIT 10 MIDPOINT OF A LINE SEGMENT 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) 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 B Fig Fig Fig 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 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 We have: MK = NK = MN = = 2.5(cm) 2 How to draw the midpoint of a line segment? ii) Folding paper: Make a midpoint on paper sheet, fold it so that sides overlap to define a midpoint A B A B A B A B A B A B A B A B A M B How to draw the midpoint of a line segment? iii) Folding rope: Using a rope to divide a straight wooden stick into two equal parts •      •  •  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 27 vi) Using compass = 2,5 A M B 28 Midpoint geometry in real life 29 DO EXERCISES Exercise 63 (Work book Page 126): Select correct answers in the following conclusions A IA = IB B AI + IB = AB C AI + IB = AB and IA = IB D AB IA=IB= WRONG WRONG RIGHT RIGHT 30 practical exercise Determine the midpoint of your pen or pencil by prepared rope You only have 30 seconds for this!!! 31 Bonus: Let H is midpoint of line segment MN, and MH=20 cm Calculate the length of line segment MN? ?cm H M N 20cm MN = 40 cm 32 Consolidating Lesson Remind : when point M is called a midpoint of line segment AB? A M M is midpoint of line segment AB B ⇔ oM is between A, B oM is equidistant from A, B (MA = MB) Do homework: 64, 65 workbook p 126 33 Thanks for your atention 34