pi form

 

A ring-shaped region is shown below. 
Its inner radius is 

12cm 

, and its outer radius is 

15cm  

 

                              Assuming you want the area of the ring.  

 

                              A_RING  =  A_{OUTER CIRCLE} – A_{INNER CIRCLE}  

 

                              A_RING  =  π * (15²) – π * (12²)   

 

                                          =  (3.14)(225) – (3.14)(144)  

 

                                          =  254.34 sq cm  

_.