semicircle

 

The semicircle below has a diameter of 20, find the area of the blue region  

 

The area of the blue region is the area of the semicircle minus the area of the big triangle.  

 

A_semicircle  =  (1/2) • π • r²  =  (1/2) • (3.14) • (100)  =  157    

 

A_{largetriangle}  =  (1/2) • base • height  =  (1/2) • (20) • (10)  = 100   

 

A_blueregion  =  157 – 100  =  57 square units   

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