BACK TO CHAPTER
Lesson 2.2

THE POWER RULE

Using limits to find derivatives is slow. Luckily, a pattern emerges that lets us differentiate polynomials in seconds.

The Shortcut

If you take the derivative of x2x^2, you get 2x2x. If you take the derivative of x3x^3, you get 3x23x^2. Do you see the pattern?

ddx(xn)=nxn1\frac{d}{dx}(x^n) = nx^{n-1}

The rule is simple: Bring the power down, then subtract one from the exponent.

Polynomial Analyzer
f(x) = x^2f'(x) = 2x^1

The Pattern

Notice how the derivative is always exactly one degree lower than the original function.

Original
x2
Derivative
2x1
Toggle the power to see how the derivative function (Red) relates to the original (Blue).

The Sum Rule

What if you have multiple terms added together?f(x)=x3+x2f(x) = x^3 + x^2.

Good news: The derivative is a linear operator. This means you can differentiate each piece separately and just add them up.

Example 1

y=x5+x3y = x^5 + x^3
y=5x4+3x2y' = 5x^4 + 3x^2

Example 2

y=3x2+10xy = 3x^2 + 10x
y=6x+10y' = 6x + 10