<PRE><B>Question 554914</B>
The area of a square = side times side.


In short, A = s times s or s^2


81 = s^2


Taking the square root of both sides, we get s = 9cm.


To find the diagonal, we use the Pathygorean Theorem.

Let d = the diagonal representing the hypotenuse of the right triangle formed by two sides of the square and the diagonal.


(side)^2 + (side)^2 = (diagonal)^2


9^2 + 9^2 = d^2


81 + 81 = d^2


162 = d^2


Taking the square root of both sides, we get d =  sqrt{162}.


The length of the diagonal is the square root of 162 
written as sqrt{162}.


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