Basic Derivative Rules — Derivative Rules: Constant, Sum,...

SECTION 1

Historical Context & Motivation

Before the rules you are about to learn existed, every single derivative had to be computed from scratch using the limit definition of the derivative. That process works, but it is painfully slow — imagine evaluating a limit every time you wanted to know how fast a car was accelerating or how quickly a population was growing. Mathematicians in the 17th and 18th centuries recognized patterns in those limit calculations and distilled them into a small set of elegant shortcut rules that make differentiation almost as fast as basic algebra.

1665

Newton's Fluxions

Isaac Newton developed his method of "fluxions" during the plague years, recognizing that rates of change could be computed systematically for polynomials and other functions.

1684

Leibniz Publishes His Calculus

Gottfried Wilhelm Leibniz published his rules for differentiation using the dy/dx notation still used today. His notation made the sum and constant multiple rules intuitive.

1748

Euler's Introductio

Leonhard Euler systematized the basic derivative rules and applied them across mathematics and physics, showing how simple rules could unlock complex problems.

1821

Cauchy Formalizes Limits

Augustin-Louis Cauchy gave rigorous limit-based proofs of the derivative rules, putting the shortcuts on a solid logical foundation that we still rely on today.

The central question these rules answer is straightforward: How can we find the derivative of a function quickly, without setting up a limit every time? The four rules in this lesson — the Constant Rule, the Sum Rule, the Difference Rule, and the Constant Multiple Rule — form the foundation that makes all future differentiation possible.

SECTION 2

Core Principles & Definitions

Each of these four rules captures a simple, common-sense idea about how rates of change behave. Before diving into the formal statements, remember that the derivative of a function f(x) — written f′(x) or df/dx — tells you the instantaneous rate of change of f at any point x. These rules let you compute that rate of change using algebra instead of limits.

Constant Rule

The derivative of any constant is zero. A constant never changes, so its rate of change is always 0. If f(x) = c, then f′(x) = 0.

Sum Rule

The derivative of a sum is the sum of the derivatives. You can differentiate each piece independently and add the results: [f + g]′ = f′ + g′.

Difference Rule

The derivative of a difference is the difference of the derivatives. Subtraction works the same way as addition: [f − g]′ = f′ − g′.

Constant Multiple Rule

A constant multiplier can be pulled out of the derivative. If you multiply a function by a number, the derivative is that number times the original derivative: [c·f]′ = c·f′.

✦ KEY TAKEAWAY

Think of differentiation like reading a speedometer. The Constant Rule says a parked car has zero speed. The Sum and Difference Rules say that if two cars are merging or separating, you can track each car's speed independently. The Constant Multiple Rule says that if a car is always going three times as fast as another, you only need to measure one car and multiply by three.

SECTION 3

Visual Explanation

The following diagram shows three functions and their derivatives to illustrate the Constant Rule, Sum Rule, and Constant Multiple Rule in action. Notice how the derivative of the constant function is the flat line at zero, how the derivative of a sum mirrors the combined behavior, and how scaling a function scales its derivative by the same factor.

Left: The constant function f(x) = 5 (dashed cyan) has derivative f′(x) = 0 (pink), a flat line on the x-axis. Center: The sum h(x) = x² + 3x (violet curve) has derivative h′(x) = 2x + 3 (amber line), matching the sum of the individual derivatives. Right: Multiplying x² by 3 makes the curve three times steeper, and the derivative is also three times larger.

In the left panel, the constant function sits flat at y = 5. Because it never rises or falls, the slope everywhere is zero — exactly what the Constant Rule tells us. In the center panel, notice how the derivative of the sum is simply the sum of each piece's derivative: the 2x comes from x² and the 3 comes from 3x. The right panel shows that tripling a function triples its derivative — the red curve and its red derivative are exactly three times the green ones.

SECTION 4

Mathematical Framework

Let's state each rule precisely with its formula. In every case, f(x) and g(x) are differentiable functions (meaning their derivatives exist), and c is any real-number constant.

CONSTANT RULE

If f(x) = c, then f′(x) = 0

c is any fixed real number. The derivative of a number that never changes is always zero.

SUM RULE

d/dx [f(x) + g(x)] = f′(x) + g′(x)

Differentiate each term separately, then add the results. This extends to sums of three or more functions as well.

DIFFERENCE RULE

d/dx [f(x) − g(x)] = f′(x) − g′(x)

Differentiate each term separately, then subtract. This is really the Sum Rule with a negative sign.

CONSTANT MULTIPLE RULE

d/dx [c · f(x)] = c · f′(x)

Pull the constant c outside the derivative, then differentiate f(x) normally. The constant acts as a multiplier on the rate of change.

💡 Power Rule Reminder

To use these rules effectively, you'll often pair them with the Power Rule: d/dx [xⁿ] = n·xⁿ⁻¹. For example, d/dx [x³] = 3x². The four rules in this lesson tell you how to handle constants, sums, differences, and scalar multiples — but the Power Rule is what you'll use to differentiate each individual xⁿ term.

SECTION 5

Detailed Breakdown with Examples

Let's see each rule applied to specific functions. The table below shows a function, the rule used, and the resulting derivative so you can see patterns emerge.

Examples of each rule applied individually and in combination

Function f(x)	Rule Applied	Derivative f′(x)
7	Constant Rule	0
−3	Constant Rule	0
5x²	Constant Multiple Rule	5 · 2x = 10x
x³ + x	Sum Rule	3x² + 1
4x³ − 2x² + x − 9	Sum, Difference, Constant Multiple, Constant	12x² − 4x + 1
−7x⁴ + 3x	Sum, Constant Multiple	−28x³ + 3

This flowchart demonstrates the full process of differentiating a polynomial. First, break it into individual terms using the Sum and Difference Rules. Then, apply the Constant Multiple Rule and Power Rule to each term. Finally, use the Constant Rule for any standalone numbers, and reassemble.

The flowchart above captures the process you'll use again and again. Every polynomial — no matter how many terms it has — can be differentiated using just these four rules plus the Power Rule. You split the polynomial apart, handle each term individually, and combine the results. With practice, you'll be able to do this in one smooth pass across the expression.

SECTION 6

Worked Example

Let's work through a complete problem step by step. We'll find the derivative of f(x) = 6x⁴ − 5x³ + 2x − 11.

Differentiate f(x) = 6x⁴ − 5x³ + 2x − 11

Step 1 — Apply the Sum and Difference RulesBreak the function into individual terms. The derivative of a sum or difference is the sum or difference of the derivatives. So f′(x) = d/dx[6x⁴] − d/dx[5x³] + d/dx[2x] − d/dx[11].

Step 2 — Apply the Constant Multiple Rule to each termPull out the constant coefficients from each term: f′(x) = 6·d/dx[x⁴] − 5·d/dx[x³] + 2·d/dx[x] − d/dx[11].

Step 3 — Apply the Power Rule to each xⁿ termUsing d/dx[xⁿ] = n·xⁿ⁻¹: d/dx[x⁴] = 4x³, d/dx[x³] = 3x², d/dx[x] = d/dx[x¹] = 1·x⁰ = 1.

Power Rule results: 4x³, 3x², and 1

Step 4 — Apply the Constant RuleThe number −11 is a constant, so its derivative is 0 by the Constant Rule: d/dx[11] = 0.

d/dx[11] = 0

Step 5 — Multiply and combineSubstitute back: f′(x) = 6·(4x³) − 5·(3x²) + 2·(1) − 0. Simplify each product: f′(x) = 24x³ − 15x² + 2.

f′(x) = 24x³ − 15x² + 2

⚡ Pro Tip

Once you get comfortable, you can combine Steps 2 and 3 mentally: just multiply the coefficient by the exponent to get the new coefficient, and reduce the exponent by one. For 6x⁴, the coefficient becomes 6 × 4 = 24 and the exponent becomes 4 − 1 = 3, giving 24x³ immediately.

SECTION 7

Strengths & Limitations

These four rules are incredibly powerful for polynomial functions, but they don't cover every situation. Understanding where they work and where they fall short will help you know when you need additional rules.

Where these rules shine and where you'll need additional tools

Strength	Limitation
Any polynomial can be differentiated term by term — no matter how long it is.	These rules alone cannot handle products of two functions, like x² · sin(x). You'll need the Product Rule for that.
They make limit computations unnecessary for standard polynomial differentiation.	Quotients of functions (like x²/(x + 1)) require the Quotient Rule, which is covered separately.
The rules work together seamlessly — you'll use multiple rules in a single problem.	Compositions like (3x + 1)⁵ look like they should use the Power Rule, but actually need the Chain Rule.
They extend naturally to functions beyond polynomials — sum and constant multiple rules work for sin, cos, eˣ, etc.	You still need to know the derivative of each basic function type (trig, exponential, etc.) separately.

✦ KEY TAKEAWAY

Think of these four rules as your basic toolkit. A carpenter doesn't just own a hammer — they need saws, screwdrivers, and drills too. The Constant, Sum, Difference, and Constant Multiple rules handle the most common jobs, but the Product Rule, Quotient Rule, and Chain Rule are waiting in the toolbox for more complex situations.

SECTION 8

Connection to Advanced Rules

The rules in this lesson are the building blocks for every other derivative rule you'll learn. The table below previews how these basic rules connect to the more advanced techniques coming next in your calculus course.

How basic rules evolve into advanced differentiation techniques

This Lesson's Rule	Advanced Extension	What It Handles
Constant Multiple Rule	Product Rule	Two variable expressions multiplied together, like x² · sin(x)
Sum/Difference Rule	Quotient Rule	A function divided by another function, like (x² + 1)/(x − 3)
All four rules	Chain Rule	Nested or composite functions, like sin(x²) or (2x + 5)⁷
All four rules	Implicit Differentiation	Equations where y is not isolated, like x² + y² = 25

Here's the encouraging truth: even when you learn the Product Rule, the Quotient Rule, and the Chain Rule, you will still use the Sum, Difference, Constant, and Constant Multiple Rules every single time. They are the foundation that never goes away. Mastering them now means every future rule will feel easier because you'll already know how to handle the pieces.

SECTION 9

Practice Problems

PROBLEM 1 — CONCEPTUAL

Explain in your own words why the derivative of a constant is zero. Use the idea of a graph to support your reasoning.

PROBLEM 2 — BASIC CALCULATION

Find the derivative of f(x) = 3x⁵ − 7x² + 4.

PROBLEM 3 — INTERMEDIATE

Find the derivative of g(x) = (1/2)x⁶ − (2/3)x³ + 8x − 100.

PROBLEM 4 — APPLIED

A ball is thrown upward, and its height in meters after t seconds is given by h(t) = −4.9t² + 20t + 1.5. Find the velocity function v(t) = h′(t), and determine the ball's velocity at t = 2 seconds.

PROBLEM 5 — CRITICAL THINKING

Suppose f(x) and g(x) are differentiable functions with f′(2) = 5 and g′(2) = −3. Without knowing the formulas for f or g, find the value of d/dx[4f(x) − 7g(x) + 10] evaluated at x = 2. Explain which rules you use and why the original formulas aren't needed.

SUMMARY

Lesson Summary

The four basic derivative rules transform differentiation from a tedious limit process into streamlined algebra. The Constant Rule tells us d/dx[c] = 0 — constants produce no change. The Sum Rule and Difference Rule let us split a function into pieces and differentiate term by term: [f ± g]′ = f′ ± g′. The Constant Multiple Rule says we can factor out any constant coefficient: [c·f]′ = c·f′.

Together with the Power Rule, these four rules let you differentiate any polynomial function quickly and accurately. They are the essential foundation for the Product Rule, Quotient Rule, and Chain Rule you will encounter next. Master these, and every future derivative technique builds naturally on what you already know.