Circles in Terms of Pi

Circumference and Area of a Circle Process steps

How do I find the circumference using the formula?

1. Determine if you are given the radius or the diameter.
2. Choose your formula. If you are given the diameter, then use 

 $C=\pi d$  If you are given the radius, use  $C=\ 2\pi r$  
3. Plug in what you know. Use 3.14 for pi. 
4. Multiply. 

**Sometimes, you will be asked to leave your answers in terms of pi. So, leave the pi symbol in your answer and multiply everything else. 

Let's try it out !!

A cruise ship has a large, circular window with a diameter of 22 meters. Approximately what is the window's circumference?

**Use 3.14 for Pi.

Now you try!!

Use your process Steps!! PUT YOUR WORK ON PAPER!

Multiple Choice

The radius of the circle is 9 meters. What is the circle's circumference?

**Use 3.14 for Pi.

• 56.52 m

• 28.26 m

• 18 m

How do I find the area using the formula?

1. Determine if you are given the radius or the diameter.  **If the diameter is given, divide it by 2 to get your radius.
2.  $A=\pi r^2$  where  $r^2=r\cdot r$  

3. Plug in what you know. Use 3.14 for pi. 
4. Multiply. 

**Sometimes, you will be asked to leave your answers in terms of pi. So, leave the pi symbol in your answer and multiply everything else. 

Find the area of a circle if the diameter is 12 inches. Use 3.14 for pi. 

• Remember your formula:

   $A=\pi r^2$  

• Notice: You are given the diameter. But, the formula uses the radius. So, you must divide the diameter by 2, to find the radius. 12/2= 6 inches.

• Now, plug in what you know. 

•  $A=3.14\left(6\right)^2$  

•  $A=3.14\left(36\right)$  

• A=113.04  $in^2$  

Multiple Choice

What is the area of this circle? Use 3.14 for pi. 

• 12.56

• 25.12

• 50.24 

• 200.96