Question

Use a sum or difference formula to find the exact value of the following.

Answer 1

Given:

`\cos (4\pi)/(7)\cos (11\pi)/(42)-\sin (4\pi)/(7)\sin (11\pi)/(42)`

The sum and difference formula is defined as,

`\begin{gathered} \text{Cos(A}+B)=\cos \text{ A cos B-SinA sinB} \\ \text{Here, A= }\frac{\text{4}\pi}{7}\text{ and B=}(11\pi)/(42) \end{gathered}`

So, for the given expression,