Aturan Cosinus

\begin{equation*}
\begin{split}
BC^2 & = 4^2 + 6^2 - 2 \:.\: 4 \:.\: 6 \:.\: \cos 60^{\text{o}} \\\\
BC^2 & = 16 + 36 - 2 \:.\: 4 \:.\: 6 \:.\: \tfrac{1}{2} \\\\
BC^2 & = 28 \\\\
BC & = 2 \sqrt{7} \text{ cm}
\end{split}
\end{equation*}