As it is shown in the diagram on the right, there is a 10cm square inside the quarter of the circle.
Find the area of the shaded part
The radius is sqrt(2(10^2)) = sqrt(200) since one edge is the center and the other the edge.
Thus, 200π is the area, /4 is 50π.
The square is 100
50π-100 is your answer.
If you don't understand anything feel free to ask.