What arcsine means
Arcsine (sin⁻¹ or asin) is the inverse of the sine function. If sin(30°) = 0.5, then arcsin(0.5) = 30°. The result is always in the range -90° to 90° (or -pi/2 to pi/2 radians).
The domain of arcsine is [-1, 1] because the sine function only produces values in that range. Inputs outside this interval have no real solution.
θ = arcsin(x), where -1 ≤ x ≤ 1
Returns the angle θ in the range [-90°, 90°].