Some facts about discriminants

For the family of polynomials in one variable $P:=x^n+a_1{x}^{n-1}+\cdots +a_n$ we ask the questions at which points its discriminant set can be considered as the graph of a function of all coefficients $a_j$ but one and how its subset of points, where the discriminant set is not smooth, projects on the different coordinate hyperplanes in the space of the coefficients~$a$.