cos(x)
sin(x)
tan(x)
acos(x)
asin(x)
atan(x)
atan2(y, x)asin and acos, there are two cuts, both along
the real axis: $(-Inf, -1]$ and
$[1, Inf)$. For atan there are two cuts, both along the pure imaginary
axis: $(-1i*Inf, -1i]$ and
$[1i, 1i*Inf)$. The behaviour actually on the cuts follows the C99 standard which
requires continuity coming round the endpoint in a counter-clockwise
direction.atan2 are S4 generic functions: methods can be defined
for them individually or via the
Math group generic.atan2(y, x) returns the angle
between the x-axis and the vector from the origin to $(x, y)$,
i.e., for positive arguments atan2(y, x) == atan(y/x).Angles are in radians, not degrees (i.e., a right angle is $\pi/2$).
All except atan2 are internal generic primitive
functions: methods can be defined for them individually or via the
Math group generic.
Abramowitz, M. and Stegun, I. A. (1972). Handbook of Mathematical Functions. New York: Dover. Chapter 4. Elementary Transcendental Functions: Logarithmic, Exponential, Circular and Hyperbolic Functions