I'm confused as to how they got from "441 = 225 + 256 – 480 cos A" to "-40 = -480 cos A" ? Problem attached

Question

kymber · Answer

attachment

experimentx · Answer

experimentx · Answer

law of cosines

kymber · Answer

Yes, I know it's the law of cosines. What I don't understand is how they got from this step to that step. Can you explain please?

experimentx · Answer

441 - 225 - 256 = -40

kymber · Answer

Why isn't it 441-1?

anonymous · Answer

$$441 = 225 + 256 – 480 cos A$$
$$441=481-480\cos(A)$$
$$441-481=-480\cos(A)$$ 
$$-40=-480\cos(A)$$ etc

anonymous · Answer

-480 is the coefficient of $\cos(A)$

kymber · Answer

Oh, so they have to stick together then?

anonymous · Answer

like 
$$4=10+6-2x$$ 
$$4=16-2x$$
$$-12=-2x$$ etc

anonymous · Answer

it is -480 times the cosine of A

kymber · Answer

Oh! Thanks for explaining it like that. I understand noooow :D