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Section 4.6 Integrals

Subsection 4.6.1 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 that the definite integral is linear. The indefnite integral is also linear.
\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 4.6.2 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 4.6.3 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 4.6.4 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 4.6.5 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 4.6.6 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*}