To answer the question about the length of AB, we need to understand the relationship between segments QS, CS, and AB. However, since the question does not explain how AB is related to QS and CS, I can't give a definitive answer about AB's length.
QS and CS could be parts of a geometry problem where Q, S, and C are points on a line, with S being between Q and C, or they could be sides of a triangle, or they might be segments related in a different manner. Without further context or a diagram, it's impossible to provide the length of AB.
If you can provide additional information on how these segments are related to each other, or provide a diagram, then it would be possible to determine the relationship and calculate AB accordingly.
If AB is simply a segment that needs to be expressed in terms of x, like QS and CS, but without knowing its specific relationship to QS and CS, we cannot solve for AB in terms of x. The precise value or expression for AB can only be found if we know how it is geometrically connected to the other segments mentioned. Please provide more context or information on how these segments relate to AB.