Question

formula to transfer the sum or the difference into product​

Answer 1

see the attachment mate ✌️☺️

Answer 2

How to remember the formulae for converting sum or difference into product?

•sin α + sin β = 2 sin (α + β)/2 cos (α - β)/2 ……….

•sin α - sin β = 2 cos (α + β)/2 sin (α - β)/2 ……….

•cos α + cos β = 2 cos (α + β)/2 cos (α - β)/2 ……….

•cos α - cos β = 2 sin (α + β)/2 sin (β - α)/2 …