Click on the links below to learn more about classifying triangles by their angles and by their sides and how to calculate a missing third angle:
Triangles Classified by Their Sides:
AAAMath (interactive with score results)
Triangles Classified by Their Angles:
Both:
Math.com (Interactive-do all 4 steps!)
Mr. Herring (info and quiz game)
Illuminations (interactive visual)
CliffsNotes (info and diagrams)
Learner.org (more info and visuals)
World of Teaching (Powerpoint presentation)
Calculating the Third Angle:
AAAMath