Khan Academy
Khan Academy: Find Angles in Congruent Triangles
Given two triangles, determine whether they are congruent and use that to find missing angle measures.
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...