The tan(x) function returns value of tangent 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 tan(double x)
Returns value of tangent of x.
aa = tan(1);
aa = ; //should return -1.5574077246549
sin, cos, cot, secant, csc