  In N=1 supersymmetric SO(N)/USp(2N) gauge theories with the tree-level
superpotential W(\Phi) that is an arbitrary polynomial of the adjoint matter
\Phi, the massless fluctuations about each quantum vacuum are described by
U(1)^n gauge theory. By turning on the parameters of W(\Phi) to the special
values, the singular vacua where the additional fields become massless can be
reached. Using the matrix model prescription, we study the intersections of n=0
and n=1 branches. The general formula for the matrix model curve at the
singularity which is valid for arbitrary N is obtained and this generalizes the
previous results for small values of N from strong-coupling approach. Applying
the analysis to the degenerated case, we also obtain a general matrix model
curve which is not only valid at a special point but also on the whole branch.
