# QB64.com

## QB64 is a modern extended BASIC programming language that retains QBasic/QuickBASIC 4.5 compatibility and compiles native binaries for Windows, Linux, and macOS.

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

## Description

• The cosine_value! must be measured >= -1 and <= 1, or an error will be generated. (PRINT _ACOS(1.2) would give the result of -1.#IND, which is basically QB64’s way of telling us that the number doesn’t exist, much like 1/0 would.)
• ARCCOSINE is the inverse function of COSine, which lets us turn a COSine value back into an angle.
• Note: Due to rounding with floating point math, the _ACOS may not always give a perfect match for the COS 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 COSine and using that value to find the angle in degrees again using _ACOS:

``````
DEFDBL A-Z

INPUT "Give me an Angle (in Degrees) => "; Angle
PRINT
C = COS(_D2R(Angle)) '_D2R is the command to convert Degrees to Radians, which is what COS expects
PRINT "The COSINE of the Angle is: "; C
A = _ACOS(C)
PRINT "The ACOS 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 COSINE of the Angle is:  .5000000000000001
The ACOS of  .5000000000000001  is:  1.047197551196598
Notice, A is the Angle in Radians.  If we convert it to degrees, we discover the value is  60

``````