Question

Evaluate the product using a sum or difference of two functions, leave them in terms of sine or cosine.

2cos(56) cos(47)

Answer 1

The applicable identity is ...

... 2cos(a)cos(b) = cos(a+b) +cos(a-b)

Using a=56, b=47, this becomes ...

... 2cos(56)cos(47) = cos(103) + cos(9)