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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.

faq: Why do integrals always have a dx?

Before you try some practice problems, here is a video that answers a very common question about integrals.

Krista King Math - Why do integrals always have a dx? [4min-36secs]

video by Krista King Math

Okay, time for some practice problems. When you are finished with those, we suggest integration by substitution as your next topic.

Practice

Conversion Between A-B-C Level (or 1-2-3) and New Numbered Practice Problems

Please note that with this new version of 17calculus, the practice problems have been relabeled but they are MOSTLY in the same order. Here is a list converting the old numbering system to the new.

Integral - Practice Problems Conversion

[A01-996] - [A02-997] - [A03-998] - [A04-999] - [A05-1000] - [A06-1001] - [A07-1002] - [A08-1005] - [A09-1007]

[A10-1315] - [A11-1316] - [B01-1003] - [B02-1004] - [B03-1006]

Please update your notes to this new numbering system. The display of this conversion information is temporary.

GOT IT. THANKS!

Instructions - - Unless otherwise instructed, evaluate the following integrals, giving your answers in exact form.

Basic Problems

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

Problem Statement

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

Solution

996 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

997 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

998 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

999 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

1000 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

1001 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

1002 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

1005 solution video

video by PatrickJMT

close solution

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

Problem Statement

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

Solution

1007 solution video

video by PatrickJMT

close solution

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

Problem Statement

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

Solution

1315 solution video

video by PatrickJMT

close solution

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

Problem Statement

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

Solution

1316 solution video

video by PatrickJMT

close solution

Intermediate Problems

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

Problem Statement

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

Solution

1003 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

1004 solution video

video by Krista King Math

close solution

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

Problem Statement

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

Solution

1006 solution video

video by PatrickJMT

close solution
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