Jawabanmu

2013-12-22T10:41:04+07:00
\cos (x-y)=\cos x.\cos y+\sin x.\sin y

cos x cos y kan udah ada di soal, tinggal dicari yg sin x.sin y
krn soal mu nda' lengkap, sy anggap x+y= \frac{\pi}{6} = \frac{180}{6}=30^0
\cos (x+y)=\cos x.\cos y-\sin x.\sin y
\cos (30)=(\frac{3}{4})-\sin x.\sin y
\frac{1}{2} \sqrt{3} =\frac{3}{4}-\sin x.\sin y\\
\sin x.\sin y=\frac{3}{4}-\frac{1}{2} \sqrt{3}\\
\sin x.\sin y=\frac{3-2 \sqrt{3}}{4}

\cos (x-y)=\cos x.\cos y+\sin x.\sin y
\cos (x-y)= \frac{3}{4} +\frac{3-2 \sqrt{3}}{4}
\cos (x-y)= \frac{6-2 \sqrt{3}}{4}