The cos(x) function returns value of cosine for each value of the given x. This and other trigonometric functions can take values in radians, degrees, and gradian. The units are determined by the system.math.angularunits object property (which can also be set in the Options dialog box).
double cos(double x)
Returns value of cosine of x.
cos(10) = ; //should return -0.83907152907645
sin, tan, cot, secant, csc