Question 215349
Since the perimeter of the square is 20 cm, then each side = {{{20/4 = 5}}} cm

By letting diagonal equal D, and using the Pythagorean formula, {{{a^2 + b^2 = c^2}}}, we get: {{{5^2 + 5^2 = D^2}}}

{{{D^2 = 50}}} ------- {{{D = sqrt(50)}}} = 7.07

Therefore, length of the diagonal, or D = {{{highlight_green(7.07)}}} cm.