Curated OER
Math Handbook: Trigonometry
You'll be spinning in unit circles once you read through this jumbo-sized resource of everything you need to know about trigonometry. Each page has color-coded examples with explicit directions that detail the problems and...
Other
University of Cambridge: Spherical Trigonometry
Very good site that acts as a tutorial/review site on Spherical Trigonometry. Many diagrams and formulas are included.
Johan Claeys
Math Abundance: Trigonometry: The Sine Function
Definition of a sine function. Range and period also are given. Graph of sine function given as well.
Purple Math
Purplemath: Inverses of Trigonometric Ratios
You know that you can take side lengths and find trig ratios, and you know you can find trig ratios (in your calculator) for angles. What is missing is a way to go from the ratios back to the original angles. And that is what "inverse...