Asin()
Returns the arcsine of <number>. The value returned will be expressed in <units>.
<units> may be 'radians', 'degrees', or 'gradians' or just the first letter of any of these. By default, <units> is 'radians'.
In a circle, there are 2*pi() radians, 360 degrees, and 400 gradians.
Example
> say asin(0)
You say, "0"
> say asin(1)
You say, "1.5707963267948966"
> say asin(fdiv(sqrt(2),2),d)
You say, "45"
> say asin(0.5,d)
You say, "30"