Derivative - Limit

Limits

Definition and Standard Limit Forms

A limit describes the value that a function approaches as the input approaches a certain point. Limits are foundational in calculus and help define continuity, derivatives, and integrals.

Basic Properties

  • \[ \lim(x + y - z) = \lim x + \lim y - \lim z \]
  • \[ \lim(xyz) = \lim x \cdot \lim y \cdot \lim z \]
  • \[ \lim\left(\frac{x}{y}\right) = \frac{\lim x}{\lim y} \]
  • \[ \lim_{x \to \alpha} [cf(x)] = c \cdot \lim_{x \to \alpha} f(x) \]
  • \[ \lim_{x \to \alpha} [f(x)]^n = \left(\lim_{x \to \alpha} f(x)\right)^n \]

Limits Involving Exponentials and Logarithms

  • \[ \lim_{x \to \infty} e^x = \infty \quad,\quad \lim_{x \to -\infty} e^x = 0 \]
  • \[ \lim_{x \to 0} a^x = 1 \]
  • \[ \lim_{x \to \infty} \ln x = \infty \]
  • \[ \lim_{x \to 0} \frac{a^x - 1}{x} = \ln a, \quad a > 0 \]
  • \[ \lim_{x \to 0} \frac{x}{\log_a(1 + x)} = \frac{1}{\log_a e} \]

Limits Approaching Infinity

  • \[ \lim_{x \to \infty} \frac{c}{x^n} = 0 \quad (n > 0) \]
  • \[ \lim_{x \to \infty} \frac{x}{x \sqrt{x!}} = e \]
  • \[ \lim_{x \to \infty} \left(1 + \frac{k}{x}\right)^x = e^k \]
  • \[ \lim_{x \to \infty} \left(1 - \frac{1}{x}\right)^x = \frac{1}{e} \]
  • \[ \lim_{x \to \infty} \left(\frac{\sqrt{2\pi x}}{x!}\right)^{1/x} = e \]
  • \[ \lim_{x \to \infty} \frac{x}{x^{e^{-x}} \sqrt{x}} = \sqrt{2x} \]

Standard Trigonometric and Inverse Limits

  • \[ \lim_{x \to 0} \frac{\sin x}{x} = 1 \quad,\quad \lim_{x \to 0} \frac{\tan x}{x} = 1 \]
  • \[ \lim_{x \to 0} \frac{1 - \cos x}{x} = 0 \quad,\quad \lim_{x \to 0} \frac{1 - \cos x}{x^2} = \frac{1}{2} \]
  • \[ \lim_{x \to 0} \frac{\arcsin x}{x} = 1 \quad,\quad \lim_{x \to 0} \frac{\arctan x}{x} = 1 \]
  • \[ \lim_{x \to 1} (\arccos x)^2 = 2 \]

Terminology

  • Limit: The value a function approaches as the input approaches a specific value.
  • Approaches: Getting closer to a number from either direction on the number line.
  • Indeterminate form: An expression like \( \frac{0}{0} \) or \( \infty - \infty \) where limits require deeper analysis.
  • Infinity (\( \infty \)): A concept of being unbounded or limitless.
  • One-sided limits: Limits from only one side (left-hand or right-hand limit).

Applications

  • Fundamental to calculus: defines derivatives and integrals.
  • Used in physics to model instantaneous velocity and acceleration.
  • Essential in economics for calculating marginal cost and profit.
  • Helps analyze rates of change in biology, chemistry, and population models.
  • Used in machine learning and numerical methods for convergence analysis.
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