Solution :
The formula of cos C – cos D is 2 sin(\(C + D\over 2\)) sin(\(D – C\over 2\)).
Example : Express cos \(6\theta\) – cos \(8\theta\) as a product.
Solution : We have,
cos \(6\theta\) – cos \(8\theta\) = 2 sin(\(6\theta + 8\theta\over 2\)) sin(\(8\theta – 6 \theta\over 2\))
= 2 sin \(7\theta\) sin \(\theta\)
Similar Formulas
What is the Formula of Sin C + Sin D ?
