The Exponential Function
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1 · Prerequisites
Abstract Algebra
Linear Algebra
Real Analysis
- Absolute and Conditional Convergence; Rearrangement; Products
- Construction of the Real Numbers via Cauchy Sequences
- Construction of the Real Numbers via Dedekind Cuts
- Continuity, IVT, EVT, and Uniform Continuity
- Countability and Uncountability
- Foundations of the Real Numbers for Analysis
- Limits of Real Functions
- limsup, liminf, and Subsequential Limits
- Monotone Functions, Discontinuities, and Continuity Sets
- Monotone Sequences, Bolzano-Weierstrass, and Cauchy Completeness
- Power Series and Real-Analytic Functions
- Properties of the Integral and the Working FTC
- Roots, Rational Powers, and Classical Inequalities
- Sequences and Limits
- Sequences and Series of Functions; Uniform Convergence
- Series: Convergence and the Nonnegative Tests
- Suprema and Infima
- The Derivative and the Mean Value Theorems
- The Riemann Integral: Definition and Integrability
- Topology of ℝ
Set Theory
2 · Logical flowchart
3 · Items
Definition
The real exponential function and the number e by a power series
Lemma
The exponential series converges absolutely for every real argument
Theorem
The exponential addition formula exp(x+y)=exp(x)exp(y)
Corollary
The exponential is positive and satisfies exp(-x)=1/exp(x)
Theorem
The exponential function is smooth and (exp)'=exp
Theorem
The exponential function is strictly increasing
Theorem
The exponential tends to +∞ at +∞ and to 0 at -∞
Corollary
The exponential is a continuous bijection from ℝ onto (0,∞)
Theorem
The exponential dominates every fixed nonnegative integer power at +∞
Theorem
The exponential is the unique solution of y'=y with y(0)=1
Theorem
Regular normalized multiplicative Cauchy equations characterize the exponential
Lemma
For fixed k, C(n, k)/nᵏ tends to 1/k!
Theorem
For every real x, (1+x/n)ⁿ→exp x
Theorem
Picard iteration from 1 produces the exponential partial sums
Theorem
The power-series, product-limit, IVP, functional-equation, and Picard definitions agree
Lemma
A geometric bound for tails of the exponential series
Corollary
The elementary numerical bound 2<e<3
Theorem
The number e is irrational
Remark
The exponential roadmap and its circularity hazards
Sources
- MIT OpenCourseWare 18.100B Real Analysis, Spring 2025 full lecture notes
- J. Lebl, Basic Analysis, Logarithm and Exponential
- J. K. Hunter, An Introduction to Real Analysis, Chapter 10
- S. G. Johnson, Exponential Functions
- J. Lebl, Basic Analysis, Analytic Functions
- MIT 18.102, Chapter 4 notes
- University of Pennsylvania MATH 3600, Section 34
- Y. Vorobets, Texas A&M MATH 409 Lecture 2-07
- R. Sedgewick and P. Flajolet, Analytic Combinatorics, Asymptotic Approximations
- J. Lebl, Basic Analysis, Picard's Theorem
- MIT Proofs in Analysis and Probability, Lecture 2 notes
- LSU MATH 7230, Homework 1
- University of Michigan MATH 295 notes