Area ratio divided in sector

There is the sector OAB which is 1/4 part a circle.

Answer the following questions.

(1) Find the ratio of the area of a shadow area and the sector OAB in Fig. 1.

Noted that the straight lines OA, CD, and EF are parallel.

(2) As shown in Fig. 2, the straight line parallel to OA was drawn from each point which divided the arc AB of the sector OAB into five equally. OA is 5 cm.

Find the sum of the area of two shadow areas.

Pi is assumed to be 3.14.

Answer