According to the meaning of the question, the shaded part = a quarter is a fan-shaped area-a triangular area.

Area of triangle = length of two right-angled sides /2= product of circle radius /2

Calculate the radius of the circle according to the area of the triangle r=√20×2=2√ 10.

So sector area =π r? /4=3. 14×40/4=3 1.4

So the shadow area = 31.4-20 =11.4.