K kastamonu Oct 2012 680 4 Istanbul Jun 4, 2016 #1 According to my book: cos115+cos25=!/2(cos(115+25)+cos(115-25)) I think this is a typo. Is there a way of getting this formula? May be it meant cos115.cos25

According to my book: cos115+cos25=!/2(cos(115+25)+cos(115-25)) I think this is a typo. Is there a way of getting this formula? May be it meant cos115.cos25

skeeter MHF Helper Jun 2008 16,217 6,765 North Texas Jun 4, 2016 #2 Go to the link ... Look at #1. b. Sum and Product of sine and cosine