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Section 4.6 Integrals

Subsection 4.6.1 Definite Integration Rules

\begin{align*} \int_a^b f(x) dx \amp = - \int_b^a f(x) dx \\ \int_a^b cdx \amp = c(b-a) \\ \int_a^a f(x) dx \amp = 0 \\ \int_a^b f(x) dx + \int_b^c f(x) dx \amp = \int_a^c f(x) dx \\ f(x) \leq g(x) \amp \implies \int_a^b f(x) dx \leq \int_a^b g(x) dx \\ \int_a^b f(x) + g(x) dx \amp = \int_a^b f(x) dx + \int_a^b g(x) dx \\ \int_a^b f(x) - g(x) dx \amp = \int_a^b f(x) dx - \int_a^b g(x) dx \\ \int_a^b cf(x) dx \amp = c \int_a^b f(x) dx \end{align*}
The last three of these rules state are linearity for the definite integral.

Subsection 4.6.2 Indefinite Integration Rules

The indefinite integral also satisfies linearity.
\begin{align*} \int f(x) + g(x) dx \amp = \int f(x) dx + \int g(x) dx \\ \int f(x) - g(x) dx \amp = \int f(x) dx - \int g(x) dx \\ \int cf(x) dx \amp = c \int f(x) dx \end{align*}

Subsection 4.6.3 Fundamental Theorem of Calculus

The basic idea of the fundamental theorem is that derivatives and integrals are inverse processes. These equations here are three expressions of that idea, each useful in its own context.
\begin{align*} \frac{d}{dx} \int_a^x g(t) dt \amp = g(x) \\ \int_a^b \frac{d}{dx} f(x) dx \amp = f(b) - f(a) \\ \int_a^b f(x) dx \amp = F(b) - F(a) \text{ if } F \text{ satisfies } \frac{dF(x)}{dx} = f(x) \end{align*}

Subsection 4.6.4 Integration by Parts

\begin{gather*} \int f(x) g^\prime(x) dx = f(x) g(x) - \int f^\prime(x) g(x) dx \end{gather*}

Subsection 4.6.5 Trigonometric Substitutions

\begin{align*} \amp \text{Expression} \amp \amp \text{Substitution} \amp \amp \text{Identity} \amp \amp \text{Domain} \\ \amp \sqrt{a^2-x^2} \amp \amp x = a sin \theta \amp \amp \sqrt{a^2 - x^2} = a \cos \theta \amp \amp \frac{-\pi}{2} \leq \theta \leq \frac{\pi}{2} \\ \amp \sqrt{a^2+x^2} \amp \amp x = a \tan \theta \amp \amp \sqrt{a^2 + x^2} = a \sec \theta \amp \amp \frac{-\pi}{2} \lt \theta \lt \frac{\pi}{2} \\ \amp \sqrt{x^2-a^2} \amp \amp x = a \sec \theta \amp \amp \sqrt{x^2 - a^2} = a \tan \theta \amp \amp 0 \leq \theta \lt \frac{\pi}{2} \end{align*}

Subsection 4.6.6 Integrals Used in Partial Fractions

\begin{gather*} \int \frac{1}{x-a} dx = \ln |x-a| + c \\ \int \frac{2ax + b}{ax^2+bx + c} dx = \ln |ax^2 + bx + c| + c\\ \int \frac{1}{(x-a)^2 + b^2} dx = \frac{1}{b} \arctan \left( \frac{x-a}{b} \right) + c \end{gather*}

Subsection 4.6.7 Common Indefinite Integrals

\begin{align*} \int x^ndx \amp = \frac{x^{n+1}}{n+1} + c \\ \int \frac{1}{x} dx \amp = \ln |x| + c \\ \int e^x dx \amp = e^x + c \\ \int a^x dx \amp = \frac{a^x}{\ln a}+ c \\ \int \ln x dx \amp = x \ln x - x + c \\ \int \log_a dx \amp = x \log_a x - \frac{x}{\ln a} + c \\ \int \sin x dx \amp = -\cos x + c \\ \int \cos x dx \amp = \sin x + c \\ \int \cos^2 x dx \amp = \frac{x}{2} + \frac{\sin 2x}{4} + c \\ \int \sin^2 x dx \amp = \frac{x}{2} - \frac{\sin 2x}{4} + c\\ \int \tan x dx \amp = \ln |\sec x| + c \\ \int \sec x dx \amp = \ln | \sec x + \tan x | + c \\ \int \csc x dx \amp = \ln | \csc x - \cot x | + c \\ \int \cot x dx \amp = \ln |\sin x| + c \\ \int \sec x \tan x dx \amp = \sec x + c \\ \int \csc x \cot x dx \amp = -\csc x + c \\ \int \sec^2 x dx \amp = \tan x + c \\ \int \csc^2 x dx \amp = -\cot x + c \\ \int \sinh x dx \amp = \cosh x + c \\ \int \cosh x dx \amp = \sinh x + c \\ \int \tanh x dx \amp = \ln \cosh x + c \\ \int \sech x dx \amp = \arctan | \sinh x| + c \\ \int \csch x dx \amp = \ln \left| \tanh \frac{1}{2} x \right| + c \\ \int \coth x dx \amp = \ln |\sinh x| + c \\ \int \sech x \tanh x dx \amp = - \sech x + c \\ \int \csch x \coth x dx \amp = -\csch x + c \\ \int \csch^2 x dx \amp = -\coth x + c \\ \int \sech^2 x dx \amp = \tanh x + c \\ \int \frac{1}{\sqrt{1-x^2}} dx \amp = \arcsin x + c \\ \int \frac{-1}{\sqrt{1-x^2}}dx \amp = \arccos x + c\\ \int \frac{1}{1+x^2} dx \amp = \arctan x + c \\ \int \frac{-1}{1+x^2} dx \amp = \text{arccot} x + c\\ \int \frac{1}{\sqrt{1+x^2}} dx \amp = \text{arcsinh} x + c \\ \int \frac{1}{\sqrt{x^2-1}} dx \amp = \text{arccosh} x + c\\ \int \frac{1}{1-x^2} dx \amp = \text{arctanh} x + c \\ \int \frac{1}{1-x^2} dx \amp = \text{arccoth} x + c\\ \int \sqrt{a^2 + x^2} dx \amp = \frac{1}{2} x \sqrt{a^2 + x^2} + \frac{a^2}{2} \ln \left( x + \sqrt{a^2 + x^2} \right) + c\\ \int \sqrt{x^2 - a^2} dx \amp = \frac{1}{2} x \sqrt{x^2 - a^2} - \frac{a^2}{2} \ln \left( x + \sqrt{x^2 - a^2} \right) + c\\ \int \sqrt{a^2 - x^2} dx \amp = \frac{1}{2} x \sqrt{a^2 - x^2} + \frac{a^2}{2} \arctan \left( \frac{x}{\sqrt{a^2 - x^2}} \right) + c \end{align*}