Web sites that list resources in mathematics and that link to mathmistakes.info:

• The Maths Internet Guide "Over 400 free quality websites carefully chosen for their interactivity and grouped into five search categories. Ideal for individual learning, homework, demonstrations or explorations." (enter the site and click on the category "Topics Only" for link to mathmistakes.info).
• Internet4Classrooms "Helping Teachers Use the Internet Effectively" (click "Links for K-12 Teachers" > "Math Topics" (and then also "General Math" and "Secondary") for links to mathmistakes.info).
• Karl's Calculus Tutor "A place for a 1st year calculus student to come when he or she needs a helping hand" (click "Cool Math Links" for link to mathmistakes.info).
• Cool Math Sites page of Mrs. Heal's Homepage (the web pages of a teacher in the Kent County (Maryland) Public School system).
• Homeschool Math, a comprehensive math resource designed for homeschooling parents and teachers (Click on "Math help" in the "Online Math Resources" section on the right side of the page for link to mathmistakes.info).

(If your site links to mathmistakes.info, please send email to comments[at]mathmistakes[dot]info with the URL of the linking page to get added to the list above.)

Web sites that discuss trigonometry:

• Trigonometry page at mathworld
• Trigonometric functions at maths online, a project of the University of Vienna
• Trigonometric Functions by David A. Joyce, Clark University
• Trigonometric Functions and Calculus for Liberal Arts and Business Majors by Stefan Waner and Steven R. Costenoble, Hofstra University
• Trigonometry at Syvum.com

Web sites that provide general information on algebra, trigonometry, calculus and other areas of mathematics:

• mathworld An online encyclopedia of mathematics
• Mathwords Terms and Formulas from Algebra I to Calculus
• Purplemath An extensive algebra resource
• Paul's Online Math Notes Online notes and tutorials by Paul Dawkins, Lamar University

Web sites that specifically discuss algebra mistakes/errors:

• The Most Common Errors in Undergraduate Mathematics A web page written by Eric Schechter, a professor at Vanderbilt University
• Algebra Review Harvey Mudd College Online Mathematics tutorial
• Top Algebra Errors A web page written by Thomas L. Schofield, a professor at Calvin College

If you want more help than you can find on mathmistakes.info or on other web sites, one source of more information is in good old fashioned books.