Types of Numbers
https://www.youtube.com/watch?v=6YytojexiOg
Determine relative min, max, domain, range, and zeros from a graph
http://wmueller.com/precalculus/ (excellent)
http://betterexplained.com/articles/a-gentle-introduction-to-learning-calculus/
Patterns
http://naturalmath.com/2015/07/root-differences/
square root 2
https://www.youtube.com/watch?v=5sKah3pJnHI