\begin{equation*}
\begin{split}
& \sin 450^{\text{o}} \:.\: \cos 750^{\text{o}} \\\\
& \sin (360 + 90)^{\text{o}} \:.\: \cos (360 \:.\: 2 + 30)^{\text{o}} \\\\
& \sin 90^{\text{o}} \:.\: \cos 30^{\text{o}} \\\\
& 1 \:.\: \frac 12 \sqrt{3} \\\\
& \frac 12 \sqrt{3}
\end{split}
\end{equation*}
