Answer:
[tex]\frac{9\sqrt{2} }{2}[/tex] cm.
Step-by-step explanation:
A diagonal of a square + two of its sides creates a 45-45-90 triangle. The relation between the lengths of said triangle is 1:1:√2. In this case the diagonal is the √2 of the ratio.
That means that the side length should be 18/√2, as this times √2 makes 18.
18/√2 simplifies to (18√2)/2 = (9√2)/2.
