asin

(asin <z>) computes the principal value of the arc sine of <z>. A domain error occurs for arguments not in the range [-1, +1]. The arc sine in the range [-pi/2, +pi/2] radians is returned.

Example:

[1] (asin 0.25)
0.25268
[2] (asin 1)
1.5708
[3] (* (asin 1) 2)
3.14159
[4]