\Header{Trig}{Trigonometric Functions}
\alias{acos}{Trig}
\alias{asin}{Trig}
\alias{atan}{Trig}
\alias{atan2}{Trig}
\alias{cos}{Trig}
\alias{sin}{Trig}
\alias{tan}{Trig}
\keyword{math}{Trig}
\begin{Description}\relax
These functions give the obvious trigonometric functions.  They
respectively compute the cosine, sine, tangent, arc-cosine, arc-sine,
arc-tangent, and the two-argument arc-tangent.
\end{Description}
\begin{Usage}
\begin{verbatim}
cos(x)
sin(x)
tan(x)
acos(x)
asin(x)
atan(x)
atan2(y, x)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x, y}] numeric vector
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The arc-tangent of two arguments \code{atan2(y,x)} returns the angle
between the x-axis and the vector from the origin to \eqn{(x,y)}{},
i.e., for positive arguments \code{atan2(y,x) == atan(y/x)}.

Angles are in radians, not degrees (i.e., a right angle is
\eqn{\pi/2}{}).

All except \code{atan2} are generic functions: methods can be defined
for them individually or via the \code{\Link{Math}} group generic.
\end{Details}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
\end{References}

