\begin{tikzpicture}
  \draw (0, 0) to (0.866025404, 0.5);
  \end{tikzpicture}

  \begin{tikzpicture}
  \draw (0, 0) to (\pgfmathsin{60}, \pgfmathcos{60});
  \end{tikzpicture}

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}

\begin{tikzpicture}
\coordinate [label=left:$A$] (A) at ( 0 , 0 );
\coordinate [label=right:$B$] (B) at ( 1 . 25 , 0 . 25 );
\draw (A) -- (B);
\node [fill=red,inner sep=1pt,label=above:$D$] (D) at
($ (A) ! . 5  ! (B) ! {sin( 60 )* 2 } !  90 :(B) $) {};
\draw (A) -- (D) -- (B);
\end{tikzpicture}

\end{document}

\begin{tikzpicture}
\draw (0, 0) to ($({sin(30)}, {cos(30)})$)
             to ($({sin(-30)}, {cos(-30)})$)
             to (0, 0);
\end{tikzpicture}