Look, there is a circular area of 1/4, and there are two circular areas of 1/4. Their sum is 1/2.

So the area of 1/2 circle is: 1/2 Uyghur r 2 = 1/2 Uyghur * A 2.

After this addition, the black part is repeated.

So subtracting the square area is the area of the black part.

So 1/2 A 2-A 2 = (Uighur /2- 1) A 2.