## Elementary Geometry for College Students (6th Edition)

Since there are all 90 degree angles and since the sides of the shape are all congruent, it is a square. We know the diagonal creates a 45-45-90 triangle, so: $s = 10 \times \frac{\sqrt{2}}{2} = 5\sqrt{2}$ Thus, we find area: $A=s^2 = (5\sqrt{2})^2 = 25 \times 2 = 50$