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56 lines
2.2 KiB
Markdown
56 lines
2.2 KiB
Markdown
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The [_ACOS](_ACOS) function returns the angle measured in radians based on an input [COS](COS)ine value ranging from -1 to 1.
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## Syntax
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> radian_angle! = [_ACOS](_ACOS)(cosine_value!)
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## Description
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* 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.)
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* ARCCOSINE is the inverse function of [COS](COS)ine, which lets us turn a [COS](COS)ine value back into an angle.
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* 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](DOUBLE) or [_FLOAT](_FLOAT) precision variables instead of [SINGLE](SINGLE).
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## Availability
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* Version 1.000 and up.
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## Example(s)
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Converting a radian angle to its COSine and using that value to find the angle in degrees again using _ACOS:
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```vb
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DEFDBL A-Z
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INPUT "Give me an Angle (in Degrees) => "; Angle
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PRINT
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C = COS(_D2R(Angle)) '_D2R is the command to convert Degrees to Radians, which is what COS expects
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PRINT "The COSINE of the Angle is: "; C
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A = _ACOS(C)
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PRINT "The ACOS of "; C; " is: "; A
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PRINT "Notice, A is the Angle in Radians. If we convert it to degrees, the value is "; _R2D(A)
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```
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```text
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Give me an Angle (in Degrees) => ? 60
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The COSINE of the Angle is: .5000000000000001
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The ACOS of .5000000000000001 is: 1.047197551196598
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Notice, A is the Angle in Radians. If we convert it to degrees, we discover the value is 60
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```
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## See Also
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* [_D2G](_D2G) (degree to gradient, [_D2R](_D2R) (degree to radian)
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* [_G2D](_G2D) (gradient to degree), [_G2R](_G2R) (gradient to degree
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* [_R2D](_R2D) (radian to degree), [_R2G](_R2G) (radian to gradient
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* [COS](COS) (cosine), [SIN](SIN) (sine), [TAN](TAN) (tangent)
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* [_ASIN](_ASIN) (arc sine), [ATN](ATN) (arc tangent)
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* [_ACOSH](_ACOSH) (arc hyperbolic cosine), [_ASINH](_ASINH) (arc hyperbolic sine), [_ATANH](_ATANH) (arc hyperbolic tangent)
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* [_ATAN2](_ATAN2) (Compute arc tangent with two parameters)
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* [_HYPOT](_HYPOT) (hypotenuse)
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*[Mathematical Operations](Mathematical-Operations)
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