Does $\cos(x+y)=\cos x + \cos y$? Find the value using a calculator: $\cos 75°$
At first I thought all I need is to separate the simpler known values like this:
$\cos 75^\circ = \cos 30°+\cos45° = {\sqrt3}/{2} + {\sqrt2}/{2}  $
$= {(\sqrt3+\sqrt2)}/{2}  $ This is my answer which translates to= $1.5731$ by calculator
However, when I used the calculator directly on $\cos 75°$, I get $0.2588$.
Where I am going wrong?

You can simply plot $cos(x+y)-(cos(x)+cos(y))$ to have your answer:

