Skip to main content
Let’s start with a few definitions and notation. A derivative represents the instantaneous rate of change of a function. The process of finding a derivative is called differentiation. If f(x) denotes a function, then f'(x) denotes its derivative — the instantaneous rate of change of f at x. Understanding derivatives is essential for physics, engineering, machine learning, and computer vision.
The image explains the concepts of derivatives and differentiation along with notation examples, and features a woman presenting on the right side.
Constant functions If a function is constant — for example f(x) = 6 — its value does not change as x changes. The derivative measures change, so the derivative of a constant is zero: 
f(x) = 6
f'(x) = 0
The image shows a presentation slide about derivatives, specifically a horizontal line with no slope or change, illustrating the function ( f(x) = 6 ). A person stands to the right of the slide.
Linear functions and slope For a straight-line function the rate of change is constant. The derivative of a linear function equals its slope, computed as rise over run (vertical change divided by horizontal change). For example, f(x) = 3x has slope 3: if the rise is 3 and the run is 1, the slope is 3. If f(x) models distance over time, the speed is constant.
The image shows a diagram explaining the derivative of a linear function, featuring the equation ( f(x) = 3x ) and a graph with a straight line and slope arrows. A person is gesturing next to the diagram.
Visualizing distance and speed for a linear function helps connect math to intuition: distance grows linearly and speed (derivative) is constant.
The image depicts a visual explanation of the derivative of a linear function, with two graphs showing distance and speed over time, along with a person presenting the content.
Non-linear functions and tangents For non-linear functions the slope varies with x. To find the slope at a specific point we draw the tangent line — the straight line that just touches the curve at that point — and measure its slope there. Consider the quadratic f(x) = x^2. The slope (derivative) differs at various x values:
  • At x = −1, the tangent slopes downward: f'(−1) = −2.
  • At x = 0, the tangent is horizontal: f'(0) = 0.
  • At x = 1, the tangent slopes upward: f'(1) = 2.
Plotting these derivative values against x yields f'(x) = 2x — the derivative of x^2. When f(x) represents distance and f'(x) represents velocity, the steepness of the distance graph corresponds to speed: steep = fast, flat = slow, zero slope = stopped. A sign change in the derivative indicates a change in direction. For higher powers the pattern continues. Example: for f(x) = x^3, the derivative is f'(x) = 3x^2. The distance and derivative graphs together capture slowing, stopping, and speeding up.
The image shows a comparison of a cubic function ( f(x) = x^3 ) and its derivative ( f'(x) = 3x^2 ) with corresponding graphs. A person is present on the right side of the image.
The power rule From these examples we arrive at the power rule — a compact, efficient recipe for differentiating polynomials. 
If f(x) = x^n, then f'(x) = n x^(n-1)
Apply the power rule to f(x) = x^4 and you get f'(x) = 4x^3.
The image features a presentation on calculus, specifically the power rule for derivatives, with a speaker gesturing, wearing a "KodeKloud" shirt.
Common extensions and rules The power rule pairs with two common, useful extensions:
  • Constant multiple rule: if a constant a multiplies the power, multiply the coefficient by the power. 
    f(x) = a x^n
f'(x) = a * n x^(n-1)
    Example: f(x) = 5x^3 → f'(x) = 15x^2.
  • Linearity (sum rule): differentiate each term separately. Example: 
    f(x) = 4x^3 + 5x^2 − 7
d/dx[4x^3] = 12x^2
d/dx[5x^2] = 10x
d/dx[−7] = 0
So f'(x) = 12x^2 + 10x
Quick reference table
RuleFormulaExample
Power ruled/dx[x^n] = n x^(n-1)d/dx[x^4] = 4x^3
Constant multipled/dx[a·g(x)] = a·g'(x)d/dx[5x^3] = 5·3x^2 = 15x^2
Sum/Differenced/dx[g(x) ± h(x)] = g'(x) ± h'(x)d/dx[4x^3 + 5x^2] = 12x^2 + 10x
Constantd/dx[c] = 0d/dx[7] = 0
Back to the car example Suppose the distance-to-roadworks as a function of time is: 
f(x) = x^2 - 80x + 400
Differentiate term-by-term using the power rule: 
f'(x) = 2x - 80
The derivative f'(x) gives the instantaneous rate of change of distance with respect to time. For instance: 
f'(0) = 2*0 - 80 = -80
f'(0) = -80 means the distance is decreasing at 80 units per time unit at x = 0. The derivative is a signed rate (negative indicates motion toward the roadworks). Speed, as commonly used, is the non-negative magnitude of velocity.
The image features a graph displaying a parabolic curve representing distance over time, with a derivative calculation and a question about negative speed. There is also a person gesturing, a cartoon cat, and a road with a car and cones at the bottom.
Find when the instantaneous rate is zero by solving f'(x) = 0: 
2x - 80 = 0
=> x = 40
So f'(40) = 0. At x = 40 seconds the distance is neither increasing nor decreasing — the car is at its closest point to the roadworks. Before x = 40 the distance is decreasing (f'(x) < 0); after x = 40 it is increasing (f'(x) > 0).
The image shows a distance-time graph with an analysis indicating speed changes at 40 seconds, and a person standing next to it.
Why derivatives matter (applications) Derivatives are fundamental across engineering and computer science. Examples:
  • Self-driving cars
    • compute instantaneous speed and direction (is distance increasing or decreasing),
    • decide braking or acceleration,
    • smooth acceleration/braking for comfort,
    • predict trajectories for safe lane changes and collision avoidance.
  • Computer vision and machine learning
    • an image is a grid of pixel intensities (e.g., 0 to 255),
    • computing differences between neighboring pixels approximates discrete derivatives,
    • these discrete derivatives highlight edges and motion (sharp local changes appear as peaks),
    • repeated derivatives across rows/columns help detect shapes and moving objects.
Summary
  • A derivative measures how fast a quantity changes at a point.
  • The power rule (f(x) = x^n → f'(x) = n x^(n-1)) makes differentiating polynomials quick and systematic.
  • Interpreting derivatives connects math to real-world systems (self-driving cars) and machine perception (edge detection).
Further reading and references

Watch Video