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What is the limit definition of a derivative and how is it used?

The limit definition of a derivative is the finite real limit of the difference quotient as the nonzero increment tends to zero. At an interior point where this limit exists, it represents the derivative and the tangent slope.

Conditions

  • A finite real derivative limit must exist at the point.
  • The point is interior and Δx≠0Δx\ne 0 while taking the limit.

Reasoning, step by step

  1. Form the difference quotient using a nonzero increment Δx.
  2. Take the limit as Δx approaches zero.
  3. Evaluate the resulting finite real limit to find the derivative and tangent slope.

Example

The source recalls the formula lim⁡Δx→0f(x+Δx)−f(x)Δx\lim_{\Delta x \to 0} \frac{f(x+\Delta x) - f(x)}{\Delta x} to define the derivative at an interior point.

Common misconceptions

  • Thinking the source proves the power rule from this definition; the material explicitly states it does not prove the power rule from it.

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Answers are generated from source material and independently checked. Consult the original video or creator if something is unclear.