find the length of side x in simplest radical form with a rational denominator.

======================================================
Explanation:
Both legs are the same length, as indicated by the tickmark.
Use the pythagorean theorem to solve for x
[tex]a^2+b^2 = c^2\\\\( \sqrt{10} )^2 + ( \sqrt{10} )^2 = x^2\\\\10 + 10 = x^2\\\\x^2 = 20\\\\x = \sqrt{20}\\\\x = \sqrt{4*5}\\\\x = \sqrt{4}*\sqrt{5}\\\\x = 2\sqrt{5}\\\\[/tex]