Elementary Geometry for College Students (7th Edition)

We find the area of the circle: $A = \pi r^2 = \pi(3.5\sqrt{2})^2 \approx 77$ We find the area of the square. Since each triangle formed is a 45-45-90 triangle, we obtain that if the diagonal has length $3.5\sqrt2$, the sides must have length 7. Thus: $A = 7^2 = 49$