1. 1.11 Day 3 Bell Ringer Please grab your calculators on
your way into the room and start
on the Bell Ringer.
1.11 Day 3
Bell Ringer
(1) Find a pair or group of angles that have an invariant sum of 180°.
(2) If you move point D along line C, will the area of ΔDEF change.

2. CD = DA (b/c D is the midpoint of AC)
What relationship do you see between the lengths of CD and DA, as well as AE and EB?
CD = DA (b/c D is the midpoint of AC)
AE = EB (b/c E is the midpoint of AB)

3. DE CB
Compare the lengths of segment DE and segment CB as you drag one of the vertices.
As segment CB gets larger, so does segment DE. DE CB
2DE = CB or 1/2CB = DE
= ½

4. What invariants did you find in ΔABC as you moved one of the vertices?
A segment connecting the midpoints of two sides of a triangle is parallel to the third side and is half its length.
Midline Conjecture
AD/AC
AE/AB
DE/CB
Area of Δ AED
Δ ABC
What invariants did you find in ΔABC as you moved one of the vertices?

5. What is the length of segment AD, EC and BC?5 D 7 4 E B C

6. What is the length of segment AD, DB, EC, and DE12 E D C 14 25 B

7. Homework Given that DE is a midline:
If DE = 10, find the length of CB.
If CB = 10, find the length of DE.
If AC = 14, find EC.
If AD = x + 5 and DB = 20, find the value of x and find the lengths of AD and AB.
If DE = 6 and CB = 3x – 4, find the value of x.
f) If the height of the triangle is 7cm and the base of the triangle is 6 cm. What is the area of the triangle?

8. Following slides was suppose to be 1.11 day 2 homework
 It is good review problems… also can be used today if we have time

9. 20 Sided – 3240° 9 sided – 1260° 17 sided – 2700° 1260 = 140° 9
(n)(n-3 ????????
What is the sum of the measures of the angles of following :
20-sided polygon?
9-sided polygon?
17-sided polygon?
20 Sided – 3240°
9 sided – 1260°
17 sided – 2700°
What is the measure of each∠ in a 9 sided polygon?
1260
= 140° 9

10. What is the area of the shaded region?
Area of square – area of circle = shaded region
L X W
8 x 8 – ( (3.14) x 42 )
64 – = 13.76

11. 2.1 – 2.4 Quiz 
Go over the problems

15. e. parallelogram