Roman C. answered 09/28/12
Masters of Education Graduate with Mathematics Expertise
Let's say that you know two sides and say that their lengths are a, and b, and let x represent the unknown side's length. Then first of all, we have x<a+b.
Also we have a < x+b which means that x > a-b. Finally, b < x+a so x > b-a. This gives us x > Max(b-a,a-b) = |a-b|
Therefore we have our final result:
|a-b| < x < a+b