\( \newcommand{\abs}[1]{\left| \, {#1} \, \right| } \) \( \newcommand{\cm}{\mathrm{cm} } \) \( \newcommand{\sec}{ \, \mathrm{sec} \, } \) \( \newcommand{\vhat}[1]{\,\hat{#1}} \) \( \newcommand{\vhati}{\,\hat{i}} \) \( \newcommand{\vhatj}{\,\hat{j}} \) \( \newcommand{\vhatk}{\,\hat{k}} \) \( \newcommand{\vect}[1]{\boldsymbol{\vec{#1}}} \) \( \newcommand{\norm}[1]{\|{#1}\|} \) \( \newcommand{\arccot}{ \, \mathrm{arccot} \, } \) \( \newcommand{\arcsec}{ \, \mathrm{arcsec} \, } \) \( \newcommand{\arccsc}{ \, \mathrm{arccsc} \, } \) \( \newcommand{\sech}{ \, \mathrm{sech} \, } \) \( \newcommand{\csch}{ \, \mathrm{csch} \, } \) \( \newcommand{\arcsinh}{ \, \mathrm{arcsinh} \, } \) \( \newcommand{\arccosh}{ \, \mathrm{arccosh} \, } \) \( \newcommand{\arctanh}{ \, \mathrm{arctanh} \, } \) \( \newcommand{\arccoth}{ \, \mathrm{arccoth} \, } \) \( \newcommand{\arcsech}{ \, \mathrm{arcsech} \, } \) \( \newcommand{\arccsch}{ \, \mathrm{arccsch} \, } \)

17Calculus - Integrals and Integration

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The idea of integration is that integration 'undoes' the derivative, i.e. integration is the 'inverse' of differentiation. I used quotes around the word 'inverse' because in actuality differentiation and integration are mostly inverses but not completely. Let's start with what an integral is and some notation first.

What Is An Integral?

Before we get to the details of integration, let's watch a quick video on exactly what integrals are. The material in this video is covered on several 17calculus pages but the video gives you a good overview of integration, what it means and some of the notation.

Physical Chemistry - What is an integral? [7min-21secs]

As you know, if you have a function, \(g(x)\), the derivative of \(g(x)\) is written
\(\displaystyle{ \frac{d}{dx}[g(x)] = G(x) }\)
In this equation, we are using \(G(x)\) to represent the new function we get after taking the derivative. When integrating, the notation looks like this
\(\int{F(x)~dx} = f(x) + C \)
In this equation, \(F(x)\) is the function we are integrating and \(f(x)+C\) is the result. The curved vertical line \(\int{}\) and the \(dx\) are both necessary in this notation. They act like brackets to indicate what is being integrated, which we call the integrand.

Okay, so what are integrals and how do we go about calculating them? Here is a great introduction video to integrals, what they represent and the notation. This is one of the best introductory videos you will find anywhere on any topic. So your time will be well spent watching this.

Krista King Math - Integrals - Calculus [ excellent video ] [5min-55secs]

video by Krista King Math


You will notice in the equation \(f(x)+C\), we have \(+C\) at the end. We need this because the derivative of a constant is zero. When we go in reverse, it is not possible to recover constants without more information. So, we use the \(+C\) as a placeholder for an unknown constant. Here is a video that explains this very well. If you are already confident with integrals, you can easily skip this video without losing anything. But, if you need a bit more explanation with some examples, this video may help.

Khan Academy - The Indefinite Integral or Anti-derivative [9min-28secs]

In this video he starts with the derivative \( \frac{d}{dx}[x^2] = 2x \).
Then explains how to work this backwards, i.e. given \(2x\) how do you get \(x^2\). Then he shows that the derivative of \( x^2+1\) is also \(2x\) and the derivative of \( x^2+2 \) is also \(2x\). So that the derivative of \( x^2 + any~constant\) is \( 2x\), usually written \(x^2+C\) where \(C\) just represents a constant.

Then he looks at the derivative of \(y=Ax^n\) which is \( (A \cdot n) x^{n-1} \) to try to figure out what \( y=\int{x^3 ~ dx} \) is.
This is a neat way of learning integration. He then generalizes the power rule for integration from this example.

Another example: \( \int{5x^7 dx} \) He is correct about not forgetting the \(+C\). Many instructors will take off points if you leave it off.

To sum up, although his explanation is a little choppy, this is a pretty good introduction video to integration.

video by Khan Academy

Some Basic Formulas

Here are a few basic formulas that you will need for upcoming pages. You already know the derivatives of these, so the anti-derivatives should contain no surprises.

\(\displaystyle{ \int{ k~dx } = kx + C }\)

 

\(\displaystyle{ \int{ x^r~dx } = \frac{x^{r+1}}{r+1} + C }\)

\(\displaystyle{ \int{ e^x~dx } = e^x + C }\)

 

\(\displaystyle{ \int{ \frac{1}{x} dx } = \ln(x) + C }\)

\(\displaystyle{ \int{ \sin(x) ~dx} = -\cos(x) + C }\)

 

\(\displaystyle{ \int{ \cos(x) ~dx } = \sin(x) + C }\)

Notes
1. In the above list, \(k\) is a constant and \(r\) is a rational number.
2. For the natural logarithm, be careful that you understand that \( \int{ \ln(x)~ dx } \neq 1/x + C \). This is a common mistake when students are first learning integration.
3. Watch the negative on the integral for sine.
4. There are comparable anti-derivatives for the other trig functions as well. You can find those details on the trig integration page.

Okay, time for some practice problems.

Practice

Unless otherwise instructed, evaluate these integrals, giving your answers in exact form.

Basic

\(\displaystyle{\int{3x^2+2x+1~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{3x^2+2x+1~dx}}\), giving your answer in exact form.

Solution

996 video

video by Krista King Math

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\(\displaystyle{\int{3x^4+5x-6~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{3x^4+5x-6~dx}}\), giving your answer in exact form.

Solution

997 video

video by Krista King Math

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\(\displaystyle{\int{1-2x^2+3x^3~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{1-2x^2+3x^3~dx}}\), giving your answer in exact form.

Solution

998 video

video by Krista King Math

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\(\displaystyle{\int{\frac{-1}{x^2}dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{\frac{-1}{x^2}dx}}\), giving your answer in exact form.

Solution

999 video

video by Krista King Math

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\(\displaystyle{\int{\frac{3}{x^3}+2x^{3/2}-1~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{\frac{3}{x^3}+2x^{3/2}-1~dx}}\), giving your answer in exact form.

Solution

1000 video

video by Krista King Math

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\(\displaystyle{\int{x^{5/2}-\frac{5}{x^4}-\sqrt{x}~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{x^{5/2}-\frac{5}{x^4}-\sqrt{x}~dx}}\), giving your answer in exact form.

Solution

1001 video

video by Krista King Math

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\(\displaystyle{\int{\frac{3}{2}x^{1/2}+7~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{\frac{3}{2}x^{1/2}+7~dx}}\), giving your answer in exact form.

Solution

1002 video

video by Krista King Math

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\(\displaystyle{\int{1+2x-4x^3~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{1+2x-4x^3~dx}}\), giving your answer in exact form.

Solution

1005 video

video by PatrickJMT

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\(\displaystyle{\int{(x+1)(x^2+3)~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{(x+1)(x^2+3)~dx}}\), giving your answer in exact form.

Solution

1007 video

video by PatrickJMT

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\(\displaystyle{\int{-5e^x+7\sin(x)~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{-5e^x+7\sin(x)~dx}}\), giving your answer in exact form.

Solution

1315 video

video by PatrickJMT

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\(\displaystyle{\int{2e^x-1+\sin(x)\csc(x)~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{2e^x-1+\sin(x)\csc(x)~dx}}\), giving your answer in exact form.

Solution

1316 video

video by PatrickJMT

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Intermediate

\(\displaystyle{\int{\frac{2}{x^{3/4}}-\frac{3}{x^{2/3}}~dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{\frac{2}{x^{3/4}}-\frac{3}{x^{2/3}}~dx}}\), giving your answer in exact form.

Solution

1003 video

video by Krista King Math

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\(\displaystyle{\int{2x\sqrt{x}-\frac{1}{\sqrt{x}}dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{2x\sqrt{x}-\frac{1}{\sqrt{x}}dx}}\), giving your answer in exact form.

Solution

1004 video

video by Krista King Math

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\(\displaystyle{\int{\frac{3x-2}{\sqrt{x}}dx}}\)

Problem Statement

Evaluate \(\displaystyle{\int{\frac{3x-2}{\sqrt{x}}dx}}\), giving your answer in exact form.

Solution

1006 video

video by PatrickJMT

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You CAN Ace Calculus

Topics You Need To Understand For This Page

Related Topics and Links

external links you may find helpful

integrals youtube playlist

Trig Formulas

The Unit Circle

The Unit Circle [wikipedia]

Basic Trig Identities

Set 1 - basic identities

\(\displaystyle{ \tan(t) = \frac{\sin(t)}{\cos(t)} }\)

\(\displaystyle{ \cot(t) = \frac{\cos(t)}{\sin(t)} }\)

\(\displaystyle{ \sec(t) = \frac{1}{\cos(t)} }\)

\(\displaystyle{ \csc(t) = \frac{1}{\sin(t)} }\)

Set 2 - squared identities

\( \sin^2t + \cos^2t = 1\)

\( 1 + \tan^2t = \sec^2t\)

\( 1 + \cot^2t = \csc^2t\)

Set 3 - double-angle formulas

\( \sin(2t) = 2\sin(t)\cos(t)\)

\(\displaystyle{ \cos(2t) = \cos^2(t) - \sin^2(t) }\)

Set 4 - half-angle formulas

\(\displaystyle{ \sin^2(t) = \frac{1-\cos(2t)}{2} }\)

\(\displaystyle{ \cos^2(t) = \frac{1+\cos(2t)}{2} }\)

Trig Derivatives

\(\displaystyle{ \frac{d[\sin(t)]}{dt} = \cos(t) }\)

 

\(\displaystyle{ \frac{d[\cos(t)]}{dt} = -\sin(t) }\)

\(\displaystyle{ \frac{d[\tan(t)]}{dt} = \sec^2(t) }\)

 

\(\displaystyle{ \frac{d[\cot(t)]}{dt} = -\csc^2(t) }\)

\(\displaystyle{ \frac{d[\sec(t)]}{dt} = \sec(t)\tan(t) }\)

 

\(\displaystyle{ \frac{d[\csc(t)]}{dt} = -\csc(t)\cot(t) }\)

Inverse Trig Derivatives

\(\displaystyle{ \frac{d[\arcsin(t)]}{dt} = \frac{1}{\sqrt{1-t^2}} }\)

 

\(\displaystyle{ \frac{d[\arccos(t)]}{dt} = -\frac{1}{\sqrt{1-t^2}} }\)

\(\displaystyle{ \frac{d[\arctan(t)]}{dt} = \frac{1}{1+t^2} }\)

 

\(\displaystyle{ \frac{d[\arccot(t)]}{dt} = -\frac{1}{1+t^2} }\)

\(\displaystyle{ \frac{d[\arcsec(t)]}{dt} = \frac{1}{\abs{t}\sqrt{t^2 -1}} }\)

 

\(\displaystyle{ \frac{d[\arccsc(t)]}{dt} = -\frac{1}{\abs{t}\sqrt{t^2 -1}} }\)

Trig Integrals

\(\int{\sin(x)~dx} = -\cos(x)+C\)

 

\(\int{\cos(x)~dx} = \sin(x)+C\)

\(\int{\tan(x)~dx} = -\ln\abs{\cos(x)}+C\)

 

\(\int{\cot(x)~dx} = \ln\abs{\sin(x)}+C\)

\(\int{\sec(x)~dx} = \) \( \ln\abs{\sec(x)+\tan(x)}+C\)

 

\(\int{\csc(x)~dx} = \) \( -\ln\abs{\csc(x)+\cot(x)}+C\)

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What Is An Integral?

Some Basic Formulas

Practice

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Practice Instructions

Unless otherwise instructed, evaluate these integrals, giving your answers in exact form.

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