The game will show you a number of beam and loading configurations. For each case, assume that the moment equation M(x) is to be derived on the basis of a free-body diagram around A. The equation M(x) will be valid for the region 0 ≤ x ≤ L.

For some beams, however, we may prefer to develop M(x) such that it is valid for only half of the beam span, 0 ≤ x ≤ L/2. In either case, the appropriate boundary conditions must fall within the limits of x that are valid for the equation M(x).