Answer:
x²
Explanation:
let the length of the side be l
Then using Pythagoras' identity on the right triangle formed by the diagonal ( hypotenuse ) and the 2 sides
The square on the hypotenuse is equal to the sum of the squares on the other 2 sides, that is
l² + l² = x²
2l² = x² ( divide both sides by 2 )
l² =
x² ( since A of square = l² )