Power rule (derivatives)
d/dx (xⁿ) = n·xⁿ⁻¹
Bring the power down as a multiplier and reduce the power by one. Constant multiples carry through.
Symbols
- n
- any real constant power
When it applies
Any constant n, where xⁿ is defined. The derivative of a constant is 0.
Worked example
Differentiate 4x³.
- 1.d/dx (x³) = 3x²
- 2.4 × 3x² = 12x²
Answer: 12x²
Try it in the Derivative Calculator tool →Product rule
d/dx (u·v) = u′v + uv′
Differentiate one factor at a time, keeping the other unchanged, and add.
Symbols
- u, v
- functions of x
- u′, v′
- their derivatives
When it applies
Wherever both u and v are differentiable.
Worked example
Differentiate x²·sin x.
- 1.u = x², u′ = 2x
- 2.v = sin x, v′ = cos x
- 3.u′v + uv′ = 2x·sin x + x²·cos x
Answer: 2x sin x + x² cos x
Try it in the Derivative Calculator tool →Quotient rule
d/dx (u ÷ v) = (u′v − uv′) ÷ v²
For a fraction of two functions. The order on top matters: bottom times derivative of top, minus top times derivative of bottom.
Symbols
- u
- numerator
- v
- denominator
When it applies
Wherever v ≠ 0 and both are differentiable.
Worked example
Differentiate (x + 1) ÷ (x − 1).
- 1.u = x + 1, u′ = 1; v = x − 1, v′ = 1
- 2.(1·(x − 1) − (x + 1)·1) ÷ (x − 1)²
- 3.= (x − 1 − x − 1) ÷ (x − 1)² = −2 ÷ (x − 1)²
Answer: −2/(x − 1)², for x ≠ 1
Try it in the Derivative Calculator tool →Chain rule
d/dx f(g(x)) = f′(g(x)) · g′(x)
Differentiate the outer function (leaving the inside alone), then multiply by the derivative of the inside.
Symbols
- f
- outer function
- g
- inner function
When it applies
Compositions where both functions are differentiable.
Worked example
Differentiate (3x + 1)⁴.
- 1.Outer: u⁴ → 4u³, with u = 3x + 1
- 2.Inner derivative: 3
- 3.4(3x + 1)³ × 3 = 12(3x + 1)³
Answer: 12(3x + 1)³
Try it in the Derivative Calculator tool →Standard derivatives
(sin x)′ = cos x, (cos x)′ = −sin x, (eˣ)′ = eˣ, (ln x)′ = 1/x
Derivatives of the basic functions, used as building blocks with the other rules.
Symbols
- x
- the variable, in radians for trig functions
When it applies
sin and cos results assume x is in radians. ln x needs x > 0.
Worked example
Differentiate 3 sin x + eˣ − ln x.
- 1.3 × cos x = 3 cos x
- 2.eˣ stays eˣ
- 3.ln x → 1/x, so −ln x → −1/x
Answer: 3 cos x + eˣ − 1/x, for x > 0
Try it in the Derivative Calculator tool →Power rule (integrals)
∫ xⁿ dx = xⁿ⁺¹ ÷ (n + 1) + C
Raise the power by one and divide by the new power. Add a constant C for an indefinite integral.
Symbols
- n
- constant power
- C
- constant of integration
When it applies
n ≠ −1. For n = −1, ∫ 1/x dx = ln|x| + C.
Worked example
Find ∫ 6x² dx.
- 1.∫ x² dx = x³ ÷ 3
- 2.6 × x³/3 = 2x³
- 3.Add the constant
Answer: 2x³ + C
Try it in the Integral Calculator tool →Integral of 1/x
∫ 1/x dx = ln|x| + C
The case the power rule can't handle (it would divide by zero). The absolute value covers negative x.
Symbols
- C
- constant of integration
When it applies
x ≠ 0. A definite integral can't cross x = 0.
Worked example
Find ∫ 3/x dx.
- 1.3/x = 3 × (1/x)
- 2.3 × ln|x|
Answer: 3 ln|x| + C
Try it in the Integral Calculator tool →Definite integral
∫ₐᵇ f(x) dx = F(b) − F(a)
Find an antiderivative F, then subtract its value at the lower limit from its value at the upper limit. The C cancels.
Symbols
- F
- any antiderivative of f
- a, b
- lower and upper limits
When it applies
f must be continuous on [a, b].
Worked example
Evaluate ∫₀² 3x² dx.
- 1.F(x) = x³
- 2.F(2) = 8, F(0) = 0
- 3.8 − 0 = 8
Answer: 8
Try it in the Integral Calculator tool →