
From the question it is given that,
Length of Diagonal = 10 cm
Let us assume square ABCD.
Sides AB = y, BC = y, CD = y, DA = y
Diagonal AC = 10 cm
Now, consider triangle ABC
By the rule of Pythagoras theorem,
AC2 = AB2 + BC2
102 = y2 + y2
100 = 2y2
y2 = 100/2
y2 = 50
y = √50 cm
y = 5√2 cm
∴The length of the side of square is √50 cm or 5√2.