Derivative - Differentiation

Differentiation

Rules and Basic Differentials

Differentiation refers to the process of finding the differential (or derivative) of a function. It represents the infinitesimal change in the output \( dy \) with respect to an infinitesimal change in input \( dx \).

Basic Differentiation Rules

  • \[ dy = y' \, dx \] — Total differential of a function
  • \[ d(Cu) = C \, du \] — Constant multiple rule
  • \[ d(u + v - w) = du + dv - dw \] — Sum and difference rule
  • \[ d(uv) = u \, dv + v \, du \] — Product rule
  • \[ d(uvw) = (vw) \, du + (uw) \, dv + (uv) \, dw \] — Product rule extension
  • \[ d\left( \frac{u}{v} \right) = \frac{v \, du - u \, dv}{v^2} \] — Quotient rule
  • \[ d(u^n) = n u^{n-1} \, du \] — Power rule
  • \[ d(\sin u) = \cos u \, du \]
  • \[ d(\cos u) = -\sin u \, du \]

Terminology

  • Differentiation: The process of computing a derivative or differential.
  • dy/dx: The rate of change of \( y \) with respect to \( x \).
  • du: A differential (infinitesimal change) in \( u \).
  • Chain rule: A rule to differentiate composite functions via their inner derivatives.
  • Infinitesimal: A quantity that is very small, approaching zero.

Applications

  • Used in physics to compute instantaneous change in position, velocity, and acceleration.
  • Essential in engineering for solving differential equations in systems and mechanics.
  • Applies to biology for modeling population dynamics and rates of reactions.
  • Used in economics for analyzing marginal cost, utility, and growth trends.
  • Forms the base of integral calculus through reverse operations.
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