Wolfram Research
Wolfram Math World: Inverse Cosine
A site that deals with inverse cosine. Article includes the definition, formulas including the Maclaurin series for the inverse cosine function, and examples, as well as numerous links to related terms.
Clark University
Clark University: Dave's Short Trig Course
This Clark University trigonometry tutorial site features questions and answers about what students can learn from trigonometry.
Khan Academy
Khan Academy: Trigonometry: Evaluate Inverse Trig Functions
Given a sine, cosine, or tangent value, find the principle angle that has this value. In other words, find the arcsine, arccosine, or arctangent of that value. Students receive immediate feedback and have the opportunity to try questions...
Math2
Math2: Trigonometric Graphs
Sketches of the graphs of the 12 "parent," trigonometry functions are given: sine, cosine, tangent, secant, cosecant, cotangent, arcsine, arccosine, arctangent, arcsecant, arccosecant, and arccotangent.
Other
Technical Tutoring: Trigonometry: The Very Fast Review
This site is a quick review of the functions and identities in trigonometry. Very helpful site.
Other
Lifewire: Excel Tan Function: How to Find the Tangent Angle
This article shows you how to find the tangent angle using Excel. You may be able to accomplish this on a scientific calculator, but if you don't have one handy, Excel can help you make these calculations better than anything else.