Question

The question is attached

Answer 1

`cos(A - B) = cos A cos B + sin A sin B`

In this case, A is
`(\pi )/(3)` and B is
`(\pi )/(5)`, so:

`cos(\pi)/(3) cos(\pi)/(5) +sin(\pi )/(3) sin(\pi )/(5) =cos((\pi)/(3) -(\pi)/(5) ) = cos(2\pi)/(15)`

Hope that helps!