If this pertains to the Pythagorean theorem, then the answer that you would most likely to end up with is by utilizing the equation a² + b² = c² where a and b are the legs of the triangle and c is the hypotenuse. The hypotenuse refer to the longest side of the triangle while the other two would be the legs of the triangle.
When solving for the missing length, just substitute the values given to their respective places in the equation. If a length of a leg is missing, then substitute the other leg's value to either a or b, then substitute the length of the hypotenuse to c. Then solve. Solving for the hypotenuse's length would be a lot easier than the legs.
