To determine the length of the unknown side in a right triangle, we can use the Pythagorean theorem, which states:
\[ a^2 + b^2 = c^2 \]
where \( c \) is the length of the hypotenuse and \( a \) and \( b \) are the lengths of the other two sides.
However, without knowing the lengths of at least two sides of the triangle or which side is the hypotenuse, it's impossible to give a specific answer for the unknown side. If you have the lengths of the known sides or more details about the triangle, please provide that information so I can help you solve for the unknown side.