Elementary Geometry for College Students (6th Edition)

5 $in^{2}$
The length of the diagonal of the square d = $\sqrt 10$ in. We know the area of the square whose diagonal has length d is A = $\frac{1}{2} d^{2}$ therefore A = $\frac{1}{2} \sqrt 10^{2}$ = $\frac{1}{2}$ * 10 = 5 $in^{2}$