first find the diagonal of the square. it is the hypotenuse of a 10-10 45 degree right triangle so 10²+10²=c² our c²=200 or c=10√2. half of this is the radius of the circle, so the radius is 5√2 the area of the circle is then π*(5√2)²=50π. the area of the square is 100, so the shaded area it's the difference 50π-100, or about 57
