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The Functions e^x and e^jθ: Introduction

Module by: Louis Scharf. E-mail the author

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This module is part of the collection, A First Course in Electrical and Computer Engineering. The LaTeX source files for this collection were created using an optical character recognition technology, and because of this process there may be more errors than usual. Please contact us if you discover any errors.

Notes to Teachers and Students

It is essential to write out, term-by-term, every sequence and sum in this chapter. This demystifies the seemingly mysterious notation. The example on compound interest shows the value of limiting arguments in everyday life and gives e x e x some real meaning. The function ejθejθ, covered in the section "The Function of e and the Unit Circle and "Numerical Experiment (Approximating e, must be understood by all students before proceeding to "Phasors" . The Euler and De Moivre identities provide every tool that students need to derive trigonometric formulas. The properties of roots of unity are invaluable for the study of phasors in "Phasors" .

The MATLAB programs in this chapter are used to illustrate sequences and series and to explore approximations to sin θ sinθ and cos θ cosθ. The numerical experiment in "Numerical Experiment (Approximating e illustrates, geometrically and algebraically, how approximations to ejθejθ converge.

“Second-Order Differential and Difference Equations” is a little demanding for freshmen, but we give it a once-over-lightly to illustrate the power of quadratic equations and the functions ex and ejθejθ. This section also gives a sneak preview of more advanced courses in circuits and systems.

Introduction

It is probably not too strong a statement to say that the function e x e x is the most important function in engineering and applied science. In this chapter we study the function e x e x and extend its definition to the function ejθejθ. This study clarifies our definition of ejθejθ from "Complex Numbers" and leads us to an investigation of sequences and series. We use the function ejθejθ to derive the Euler and De Moivre identities and to produce a number of important trigonometric identities. We define the complex roots of unity and study their partial sums. The results of this chapter will be used in "Phasors" when we study the phasor representation of sinusoidal signals.

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