ASIN returns the inverse trigonometric sine of a number.

ASIN (`number`)

This
function returns the inverse trigonometric sine of `number`,
which is the angle (in radians) whose sine is `number`.
The angle returned is between -PI/2 and +PI/2.

`=ASIN(0)` returns `0`.

`=ASIN(1)` returns `1.5707963267949
(PI/2 radians).`.

`=DEGREES(ASIN(0.5))` returns `30`.
The sine of 30 degrees is 0.5.