On the Zeroes of the Nth Partial Sum of the Exponential Series

2. GENERAL PROPERTIES. The fundamental theorem of algebra states that any polynomial of degree N (> 0) has exactly N zeroes, provided that zeroes are counted according to multiplicity. Thus, each polynomial PN (z) has exactly N zeroes. Proposition 1. For each N ≥ 1 all zeroes of PN (z) are simple. Proof. If r were a multiple root of PN (z), then r would also be a zero of P ′ N (z) = PN−1(z). But then 0 = PN (r) − PN−1(r) = r N N ! , implying that 0 is a zero of PN (z), an obvious contradiction.