Answer:
Below in bold.
Explanation:
The diagonal forms 2 right triangles in the square,
Applying the Pythagoras Theorem to a triangle:
(12√6)^2 = x^2 + x^2 where x is the side of the square.
144*6 = 2x^2
x^2 (which is the area of the square)
= 144*6 / 2
= 144*3
= 432 cm^2.