## Wednesday, February 2, 2011

### Meldrick's Circle Surface Area Post

Here are the notes that we took down in class:

-the bases of a cylinder are circles
-the radius is half a diameter
-the diameter cuts a circle in half
-the circumference is the perimeter of a circle
-pi - the ratio between the circumference and diameter- 3.14159.. and on.. and on- you get it, right?

Here are the formulas that we also took down in class:
d/2=r

Diameter
2r=d or c/pi=d

Circumference
pi(d)=c *remember, brackets mean multiplying*

Area (of a circle)
Pi(r squared)

For example:

Here are the homework circles:

This is a link that is dedicated to circles.
Here is a link to a video that I couldn't embed.

7.3

a) When the radius of a cylinder is doubled, the volume of a cylinder is multiplied by 4.
EX.
v = π*r^2*h
v = 3.14*1²*1
v = 3.14*1*1
v = 3.14 cm³

v = π*r^2*h
v = 3.14*2²*1
v = 3.14*4*1
v = 12.56 cm³

b)When the height of a cylinder is doubled, the volume of the cylinder is doubled.
EX.
v = π*r^2*h
v = 3.14*1²*1
v = 3.14*1*1
v = 3.14 cm³

v = π*r^2*h
v = 3.14*1²*2
v = 3.14*1*2
v = 6.28 cm³

7.4

The volume of the triangular prism shown is 48 cm^3. What is the value of the missing measurement?
The value of the missing measurement is 5.
EX.
[v/h²]*2 = area of the base
[48 cm³/8 cm]*2 = area of the base
6 cm²*2 = area of the base
12 cm² = area of the base

area of the base/h¹ = base
12 cm²/4 cm = base
3 cm = base
Now, if...
h¹ = a
base = b
= c
a²+b² = c²
4²+3² = c²
16+9 = c²
25 cm² = c²
sqrt of c² = c
sqrt of 25 = c
5 = c
5 =