asin
Returns the arc sine of a value; the returned angle is in the range -pi/2 through pi/2. Special cases:
If the argument is NaN or its absolute value is greater than 1, then the result is NaN.
If the argument is zero, then the result is a zero with the same sign as the argument.
Parameters
a
the value whose arc sine is to be returned. @ return the arc sine of the argument.