Question 215356
Since the perimeter of the square is 36 cm, then each side = {{{36/4 = 9}}} cm

By letting diagonal equal D, and using the Pythagorean formula, {{{a^2 + b^2 = c^2}}}, we get: {{{9^2 + 9^2 = D^2}}}

{{{D^2 = 162}}} ------- {{{D = sqrt(162)}}} = 12.73

Therefore, length of the diagonal, or D = {{{highlight_green(12.73)}}} cm.