The Federalist. 39 - 40. In 39, Madison (as Publius) argues that the proposed Constitution represents "neither a national nor a federal Constitution, but a composition of both." In 40, he defends the convention's decision to scrap, rather than revise, the Articles of Confederation.
The Road to Reality (Roger Penrose). Section 5.3. Exponential function expressed as power series; multi-valued logarithms in the complex plane. "There are many different solutions z for a given choice of w in the relation w = e^z." Introduction of the factor 2*pi*i in the exponent, and the derivation of Euler's formula.
Visual Complex Analysis (Tristan Needham). pp. 14 - 17. Derivation of sine and cosine from Euler's formula, and geometrical interpretations.