# Question efb55

Aug 14, 2017

This can be simplified using the sum and difference formula for cosine:

$\cos \left(A - B\right) = \cos A \cos B + \sin A \sin B$

In this formula, A = 80˚ and B = 20˚, thus the given expression is equivalent to

cos(60˚)#

Which in turn is equivalent to $\frac{1}{2}$. I don't know what the rest of the question is asking.

Sorry I couldn't be of more help.