Can you find the diagonal using the law of cosines?
MartFL gave you a powerful hint.
But the answer is even simpler.
Consider the zigzag line.
We want the hypotenuse of a 4-by-8 right triangle.Code:* |. 3| . | . 4 *---.-----* : d. | : . | 5: . |5 : . | : .| * - - - - * 4
Then the side of the square is:
Therefore, the area of the square is: