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Java - Math.asin() method example

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Created by:

Jasmin

395

The Math.asin function returns number in radians in the range -Math.PI/2 to +Math.PI/2. The function calculates the inverted sine function value.

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public class CustomMath {
​
    static double calculateAngle(double a, double h) {
        return Math.asin(a / h);
    }
    
    public static void main(String[] args) {
        /*
          |\
          | \ h
        a |  \
          |__*\ <- angle
            b
        */
​
        double a, b, h;
​
        // a, b and h build isosceles right triangle
        a = 3;
        b = a;
        h = Math.sqrt(a * a + b * b);
        System.out.println( calculateAngle(a, h) ); // 0.7853981633974483 <- ~45 degrees
​
        // a, b and h build half of equilateral triangle
        a = 3;
        b = a * Math.sqrt(3);
        h = Math.sqrt(a * a + b * b);
        System.out.println( calculateAngle(a, h) ); // 0.5235987755982989 <- ~30 degrees
​
        // a, b and h are not able to build triangle
        a = 3;
        b = a;
        h = 1;
        System.out.println( calculateAngle(a, h) ); // NaN
    }
}

1. Documentation

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Syntax	xxxxxxxxxx 1 package java.lang; 2 3 public final class Math { 4 5 public static double asin(double number) { ... } 6 7 } Note: Classes in the `java.lang` package are imported automatically, so it is not necessary to do it manually - we use just `Math.asin()` call.
Parameters	`number` - double value that represents the result of the operation `adjacent / hypotenuse` on the right triangle (primitive value). `number` should be in the range `-1` to `+1`.
Result	`number` value in radians in the range `-Math.PI/2` to `+Math.PI/2` (primitive value). If the value can not be calculated `NaN` is returned.
Description	`asin` is a static method that takes only one parameter and returns an approximation of the result of the mathematical function arcsine(x).

2. Working with degrees

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xxxxxxxxxx
 
public class CustomMath {
​
    static double calculateAngle(double a, double h) {
        double angle = Math.asin(a / h);
​
        return (180 / Math.PI) * angle; // rad to deg conversion
    }
    
    public static void main(String[] args) {
        /*
          |\
          | \ h
        a |  \
          |__*\ <- angle
            b
        */
​
        double a, b, h;
​
        // a, b and h build isosceles right triangle
        a = 3;
        b = a;
        h = Math.sqrt(a * a + b * b);
        System.out.println( calculateAngle(a, h) ); // ~45 degrees
​
        // a, b and h build half of equilateral triangle
        a = 3;
        b = a * Math.sqrt(3);
        h = Math.sqrt(a * a + b * b);
        System.out.println( calculateAngle(a, h) ); // ~30 degrees
​
        // a, b and h are not able to build triangle
        a = 3;
        b = a;
        h = 1;
        System.out.println( calculateAngle(a, h) ); // NaN
    }
}
​