Question

Question in the comments
Please help

Answer 1

It asks for words in the proof behind this diagram and these equations as a a proof for the law of cosines,
\[(2a \cos x-b)b=(a-c)(a+c)\]
Translates into
\[c^2=a^2+b^2-2ab \cos x\]

Answer 2

What I really need help with is how in the first equation the one side equals the other because I need to give a proper explanation, I can do the math by myself