Area of the Circle

1. • 
     

     1. 1
        Calculate the length of the radius. If you only know (or have measured) the diameter (the distance from one side of the circle to the other), then divide it by two to obtain the radius. The radius of a normal circle is always one-half of the diameter.
        
        
        
        
     2. 2
        Read the formula. The formula for finding the area of a circle is
        
        Area equals pi multiplied by (r squared)
        
        
        
        
     3. 3
        Multiply the radius by itself to square it. For example, if your radius was 6 cm, your radius squared would be 36 cm squared.
        
        
        
        
     4. 4
        Multiply the result you get from Step 3 by pi. (Use this also in "Finding the Area of a Sector").
        
        
        
        
        • If the instructions say "leave in terms of pi" or "exactly", then just stick the pi onto your answer (for example, the area of the circle = π36 cm^2.) If you just round it to 3.14, it's not at all exact. There is no way to show it exactly besides leaving the pi sign.
        • If the instructions say anything about rounding, replace pi with 3.14 or use your calculator's pi button.
          
          Here is an example:
          
          
          
          

           If the instructions say anything about rounding, replace pi with 3.
          
          
          
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