​What are the parts of a circle?

The distance between the center of the circle and the edge is called the RADIUS

The distance from the edge of a circle, straight across the center, to the other edge, is called the DIAMETER.

The diameter is double the radius. The radius is half the diameter.

Pi is always the number 3.141592653589793238462...

It goes on forever, but in 7th grade, we will use 3.14 as an approximation for pi.

Pi - π

• The perimeter of the circle

• You can find the circumference using the formula: C=πd

• Write this formula down for every circumference problem

​Circumference

Find the circumference

1. Write down the formula: C=πd

2. Replace pi with 3.14 in the formula: C=(3.14)d

3. Replace diameter in the formula: C=(3.14)(30.2)

4. Solve the equation: C=94.828 cm

Find the circumference

1. Write down the formula: C=πd

2. Replace pi with 3.14 in the formula: C=(3.14)d

3. Turn the radius into a diameter:

   r = 14, so d = 14 x 2 = 28

4. Replace diameter in the formula: C=(3.14)(28)

5. Solve the equation: C=87.92 in

Find the diameter and radius

If you're given the Circumference, we can work backwards to find the diameter

1. Write down the formula: C=πd

2. Replace pi with 3.14: C=(3.14)d

3. Replace C with the circumference: 40.82=3.14d

4. Divide both sides by 3.14 /3.14 /3.14

5. Divide your diameter by 2 13 = d

6. That's your radius 6.5 = r

• How much space is inside a circle

• You can find the circumference using the formula: A=πr²

• r² means r x r, kind of like length times width.

​Area

Find the Area of a circle

1. Write down the formula: A=πr²

2. Replace pi with 3.14 in the formula: A=3.14r²

3. Replace radius in the formula: A=3.14(5)²

4. Square the radius: A=3.14(25)

5. Solve: A=78.5 cm²

Find the Area of a circle

1. Write down the formula: A=πr²

2. Replace pi with 3.14 in the formula: A=3.14r²

3. Determine the radius

   d = 26, so r = 26/2 = 13

4. Replace radius in the formula: A=3.14(13)²

5. Square the radius: A=3.14(169)

6. Solve: A=530.66 cm²