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Real Analysis
Limits made rigorous: sequences, series, convergence, improper integrals, complex numbers as functions.
레슨
limit of (1 + 1/n)^n as n -> oo
Core
Convergence of series
Divergence, ratio, comparison and integral tests, and the harmonic series.
does 1/n^2 for n = 1 to oo converge
Core
Improper integrals
Integrals to infinity or across a singularity, defined as limits.
integrate 1/x^2 dx from 1 to oo
Advanced
Taylor approximation and error
How well a polynomial stands in for a function, and how far you can trust it.
taylor series of sin(x)
Advanced
Functions of a complex variable
Euler's formula, and why complex analysis is where the Riemann Hypothesis lives.
e^(i*pi)
Core
Continuity and differentiability, rigorously
ε, δ continuity, the intermediate and extreme value theorems, the mean value theorem.
limit of sin(x)/x as x -> 0
Advanced
Sequences of functions and uniform convergence
Pointwise versus uniform, and when limits commute with integrals and derivatives.
taylor series of e^x
Analysis is calculus with the reasons attached: what a limit really is, when a series converges and why, what makes a function continuous or differentiable, and how the same ideas extend to the complex plane. It is the language the open problems are written in.
더 많은 레슨
Sequences and series
Functions
The real line
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사람들이 묻는 질문
What is the ε, δ definition actually saying?
That you can make the output as close to the limit as anyone demands (within ε) by keeping the input close enough (within δ). It replaces "approaches" with a challenge-and-response that can be checked.
Why does the harmonic series diverge when its terms go to zero?
Because the terms shrink too slowly: group them as 1/3 + 1/4 > 1/2, 1/5 + … + 1/8 > 1/2, and so on: infinitely many halves.
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