MathOverflow

sin(x): Sine of x (x is in radians)
cos(x): Cosine of x (x is in radians)
tan(x): Tangent of x (x is... well, you know)
asin(x): Arc sine of x (in radians)
acos(x): Arc cosine of x (in radians)
atan(x): Arc tangent of x (in radians)
sqrt(x): Square root of x. Result is NaN (Not a Number) if x is negative.
log(x): Natural logarithm of x (not base-10).
abs(x): Absolute value (magnitude) of x
ceil(x): Ceiling of x - the smallest integer that's >= x.
floor(x): Floor of x - the largest integer that's <= x
round(x): X, rounded to the nearest integer.
exp(x): ex (exponential/antilogarithm function with base e)
random(n): Get a random number in the range [0, n). If n is zero, or not provided, it defaults to 1.
fac(n): n!
min(a,b.,..): Get the smallest ("minimum") number in the list
max(a,b,...): Get the largest ("maximum") number in the list
pyt(a, b): Pythagorean function, i.e. the c in "c^2 = a^2 + b^2"
pow(x, y): This is exactly the same as "x^y".
atan2(y, x): arc tangent of x/y. i.e. the angle between (0, 0) and (x, y) in radians
PI: Ratio of a circle's circumference to its diameter.