Midline Theorem by Cher RM

1. MIDLINE
THEOREM
GRADE 9 MATHEMATICS
®ᵯ

2. Midline Theorem
The segment that joins the
midpoints of two sides of a triangle
is parallel to the third side and half
as long.

3. Midline Theorem
Midline is equal to one half of
the base of a triangle.
A
D E
B
C
DE=
𝟏
𝟐
(𝑨𝑩)

4. 1. If DE = 10.5 cm , What is AB?
A
D E
B
C
EXAMPLES!!!

5. 1. If DE = 10.5 cm , What is AB?
Answer: AB = 21 cm
A
D E
B
C
10.5=
𝟏
𝟐
(𝑨𝑩)
EXAMPLES!!!

6. 2. If BC= 32 cm , What is CE?
A
D E
B
C
EXAMPLES!!!

7. 2. If BC= 32 cm , What is CE?
Answer: CE = 16 cm
A
D E
B
C
EXAMPLES!!!

8. 3. If AB = 30 cm, What is DE?
A
D E
B
C
EXAMPLES!!!

9. 3. If AB = 30 cm, What is DE?
A
D E
B
C
DE=
𝟏
𝟐
(𝑨𝑩)
DE=
𝟏
𝟐
(𝟑𝟎)
DE= 15 cm
EXAMPLES!!!

10. 4. DE= (3x – 2) cm and AB = (9x – 13) cm,
solve for x.
A
D E
B
C
EXAMPLES!!!

11. 4. DE= (3x – 2) cm and AB
= (9x – 13) cm, solve for x.
A
D E
B
C
DE=
𝟏
𝟐
(𝑨𝑩)
3x – 2 =
𝟏
𝟐
(𝟗𝒙 − 𝟏𝟑)
6x – 4 = 𝟗𝒙 − 𝟏𝟑
6x – 9x = −𝟏𝟑 + 𝟒
– 3x = −𝟗
x = 𝟑
EXAMPLES!!!

12. 4. DE= (3x – 2) cm and AB = (9x – 13) cm, solve for x.
x = 𝟑
AB = (9x – 13) cm
DE= (3x – 2) cm

13. 4. DE= (3x – 2) cm and AB = (9x – 13) cm, solve for x.
DE = 3x – 2
x = 𝟑
DE = 3(3) – 2
DE = 7 cm
AB = (9x – 13) cm
AB = 9x – 13
AB = 9(3) – 13
AB = 14 cm
DE= (3x – 2) cm

14. “Alldreamsarewithin reach.All youhave to dois
keep movingtowardsthem”.
-Viola Davis-