Sec3 - A Math trigonometry-Addition formula by Gary Ang | Aug 18, 2015 | 16S4, Board-casts | 0 comments [vimeography id="264"] In this lesson, we practised more trigo proving questions and we started on the addition formula. Submit a Comment Cancel replyYour email address will not be published. Required fields are marked *Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ