Use online textbook to view videos & practice quizzes
http://www.mesacc.edu/~scotz47781/mat182/notes/Sum_Diff/Sum_Diff_Tan_Practice.pdf
https://www.youtube.com/watch?v=ZhvvkCa_60w
https://www.youtube.com/watch?v=hd2Tu0-Qb3k
https://www.youtube.com/watch?v=sU2pyMR8GZ4