The _ASIN function returns the angle measured in radians based on an input SINe value ranging from -1 to 1.

## Syntax

radian_angle! = _ASIN(sine_value!)

## Description

- The sine_value! must be measured >= -1 and <= 1, or else it will generate a return value of
**-1.#IND**, which is basically QB64’s way of telling us that the number doesn’t exist. - ARCSINE is the inverse function of SINe, and turns a SINe value back into an angle.
- Note: Due to rounding with floating point math, the _ASIN may not always give a perfect match for the SIN angle which generated this. You can reduce the number of rounding errors by increasing the precision of your calculations by using DOUBLE or _FLOAT precision variables instead of SINGLE.

## Availability

- Version 1.000 and up.

## Example(s)

Converting a radian angle to its SINe and using that value to find the angle in degrees again using _ASIN:

```
DEFDBL A-Z
INPUT "Give me an Angle (in Degrees) => "; Angle
PRINT
C = SIN(_D2R(Angle)) '_D2R is the command to convert Degrees to Radians, which is what SIN expects
PRINT "The SINE of the Angle is: "; C
A = _ASIN(C)
PRINT "The ASIN of "; C; " is: "; A
PRINT "Notice, A is the Angle in Radians. If we convert it to degrees, the value is "; _R2D(A)
```

```
Give me an Angle (in Degrees) => ? 60
The SINE of the Angle is: .8660254037844386
The ACOS of .8660254037844386 is: 1.047197551196598
Notice, A is the Angle in Radians. If we convert it to degrees, we discover the value is 60
```

## See Also

- _D2G (degree to gradient, _D2R (degree to radian)
- _G2D (gradient to degree), _G2R (gradient to degree
- _R2D (radian to degree), _R2G (radian to gradient
- COS (cosine), SIN (sine), TAN (tangent)
- _ACOS (arc cosine), ATN (arc tangent)
- _ACOSH (arc hyperbolic cosine), _ASINH (arc hyperbolic sine), _ATANH (arc hyperbolic tangent)
- _ATAN2 (Compute arc tangent with two parameters)
- _HYPOT (hypotenuse) *Mathematical Operations