ANSWER:
4th option: 10√2 cm
STEP-BY-STEP EXPLANATION:
With the diagonal a right triangle is formed where the hypotenuse is the diagonal, therefore we can apply the Pythagorean theorem as follows:
[tex]\begin{gathered} h^2=a^2+b^2 \\ \\ \text{ squares have equal sides a = b, therefore:} \\ \\ h^2=a^2+a^2 \\ \\ h^2=2a^2 \\ \\ \text{ we replacing:} \\ \\ 20^2=2a^2 \\ \\ a^2=\frac{400}{2} \\ \\ a=\sqrt{200} \\ \\ a=10\sqrt{2} \end{gathered}[/tex]
Therefore, the correct answer is 4th option: 10√2 cm
