## Happy with the Amazon Kindle Voyage

Recently, I hurt my eyes by spending too much time in front of a computer, so I decided to buy an alternative gadget which I can use for reading that will lessen my exposure to LED monitors. I bought a Kindle Voyage and for the past three days that I have been using it, I am very happy about it. I was able to read for a long time without taking a rest in between reads which I now do if I am using computer monitors.

If you are not familiar with this product, Amazon has produced a series of e-readers called Kindle and the three of them are Kindle, Kindle Paperwhite, and Kindle Voyage. What I like about these three readers is that their screens resembles paper (yes, they are black and white) which means that they will not hurt your eyes which usually happens in ordinary screens. They are also very handy and easy to use.  » Read more

## Free Precalculus Ebooks and Lecture Notes

I was looking for Precalculus ebooks/notes and I have found the following links. Most of these books are are licensed under Creative Commons and/or lecture notes so, I assume that they are safe to download.

As for 10, 11, and 12, the website containing the links may have obtained permission from the publisher to display it online, but I don’t think it is legal to download them.

Free Precalculus Ebooks

1. Functions Modeling Change: A Precalculus Course by Marcel B. Finan
2. PreCalculus by Carl Stitz and Jeff Zeager
3. Precalculus by Collingwood, Prince, and Conroy
4. Precalculus: An Investigation of Functions by David Lippman and Melonie Rasmussen
5. Precalculus Notes from University of Notredame
6. Precalculus Textbook from Rancocas Valley High School
7. Precalculus An Honors Course by David Santos
8. Precalculus by Thomas Tradler and Holly Carley
9. Precalculus by Ken Kuniyuki
10. Precalculus: Graphical, Numerical and Algebraic by Franklin Demana, Bert Waits, Gregory Foley and Daniel Kennedy
11. Precalculus with Limits: A Graphing Approach by Ron Larson
12. Precalculus: A Graphing Approach by Thomas Hungerford, Irene Jovel, and Betty Mayberry
13. THS Advanced Precalculus

To see more free Ebooks and other freebies, please visit the age.

Enjoy learning!

## How to Use the Factorial Notation

We have had several discussions about the factorial notation, so I think this introduction is a bit late. However, it is important that you know these basic facts in order to perform calculations and understand better in later discussions.

The factorial of a non-negative integer $n$ is the product of all the positive numbers less than $n$. For example, the

$4! = 4 \times 3 \times 2 \times 1 = 24$.

and

$5! = 5 \times 4 \times 3 \times 2 \times 1 = 120$.

In Introduction to Permutations, we have discussed that there are $n!$ ways to arrange $n$ distinct objects into a sequence. For instance, if we have 3 objects namely A, B, and C, then they can be arranged in $3! = 3 \times 2 \times 1 = 6$ ways. The arrangement are as follows:

$ABC, ACB, BAC, BCA, CAB, CBA$.

We have also learned some reasons why mathematicians chose the definition $0! = 1$. » Read more

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