jika sin a+sin b=2√A dan cos a+cos b=2√B maka cos (a+b)=...

[tex]sin (a)+sin( b)=2 \sqrt{A} \\ cos (a)+cos (b)=2 \sqrt{B} \\ cos (a+b) = 2 \sqrt{B} - 2 \sqrt{A} \\ = 2(\sqrt{B} - \sqrt{A})[/tex]