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What is asin() in D?


The asin() function, also called the arc sine function, returns the inverse sine of a number. To be more specific, it returns the inverse sine of a number in radians.

The figure below shows the mathematical representation of the asin() function.

Mathematical representation of the inverse sine function

Note: std.math is required for this function.

To convert radians to degrees, use the following formula:

degrees = radians * ( 180.0 / PI )


//number can be real, float, or double.


This function requires a number as a parameter. The parameter must be a value between -1 and 1.

  • -1 <= parameter <= 1.

  • If the value is outside -1 <= parameter <= 1, then asin() returns -NaN.

Return value

asin() returns the inverse sine of the number that is sent as a parameter in radians. The return value lies in the interval [-PI/2, PI/2] radians.


The code below demonstrates how to use the asin() function in D.

import core.stdc.stdio;
import std.stdio;
//header required for function
import std.math;

int main() {
    //positive number in radians
    writeln("The value of asin(0.5): ",asin(0.5) ," Radians");

    // negative number in radians
    writeln("The value of asin(-0.5): ",asin(-0.5) ," Radians");

    //applying asin() and then converting the result in radians to degrees
    // radians = 0.5
    // PI = 3.14159265
    double result=asin(0.5) * (180.0 / PI);
    writeln("The value of asin(0.5): ",result," Degrees");

    //error output
    writeln("The value of asin(1.5): ",asin(1.5));
    writeln("The value of asin(-1.5): ",asin(-1.5));

    return 0;


  • In lines 8 and 11, we use the asin() function to convert 0.5 to radians.
  • In line 17, we use the asin() function to convert result into degree.
  • In lines 20 and 21, we use the asin() function to show error nan.



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