Review

• Multiplying decimals: 3.2 x 5.12

• Multiplying fractions and whole numbers: 5 x 2/3

Circles, Pi, & Circumference

The outside of the circle is called

circumference

The circumference is the distance around the circle.

The midpoint of a circle is

center

The line drawn from the centre to the circumference is …

radius

The line drawn from one circumference through the centre to another

circumference is …

radius

diameter

The diameter cuts the circle in half!

A line that connects one point on the edge of the circle with another point on

the circle is called ….

chord

The chord that passes through thecentre of the circle is the diameter.

A segment ie. part of the circumference of the circle is

called an ...a r

c

Parts of the Circle

centre

radius

diameter

chord

arc

The Definition of Pi• Pi, not Pie.

• 1.The 16th letter of the Greek alphabet is P or p, corresponding to the roman p.

• 2. A number, represented by said letter, expressing the ratio of the circumference of a perfect circle to its diameter. The value of pi has been calculated to many millions of decimal places, to no readily apparent pattern.

Pi Equals?

• π = circumference/diameter

≈

• π ≈ 22/7 or 3 and 1/7

• We will use 3.14

3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273………. (on and on and on)

Use Pi to Find:

• The area of a circle = πr2

• Circumference of a Circle = πd or 2πr

• Surface Area of a Sphere, Volume of a Cone, Cylinder and Sphere all are formulas that involve π.

dCr C or 2

:is ceCircumfren find toformula The

7

22or 3.14

BACK

Find the Circumference of the circle.

rC 2

214.32C

yd. 56.12CBACK

Find the circumference using the diameter.

π dC

1014.3C

in. 4.31C

BACK

Find the circumference of the circle.

π dC

1614.3C

ft. 24.50CBACK

How would you find the diameter of a circle if you were only given the circumference? Cd

Find the diameter of a circle that has a circumference of 66.

14.366 d21d

BACK

Videos

• http://www.brainpop.com/math/numbersandoperations/pi/

• http://www.youtube.com/watch?v=8-cazxAL_tU

• http://www.youtube.com/watch?v=mZ4CP0vTgEE