Find Area of Shaded Region

you have a rectangle with sides:
the length =20
half circle has diameter 20, =>r=10
the width=10

the area of shaded region is:

the area of rectangle - the area of half circle

the area of shaded region =20*10-(10)^2*pi/2=200-50*pi
approximately:42.92 square units

 

Very cool. I like shaded region geometry problems.