What is the Formula of 2 Cos A Cos B ?

Solution :

The formula of 2 cos A cos B is cos (A + B) + cos (A – B).

Example : Solve : 2 cos 75 cos 15.

Solution : We have,

2 cos 75 cos 15 = cos (75 + 15) + cos (75 – 15)

= cos 90 + cos 60

= 0 + $$1\over 2$$

= $$1\over 2$$

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