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# Java - Math.atan() method example

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The `Math.atan` function returns number in radians in the range `-Math.PI/2` to `+Math.PI/2`. The function calculates the inverted tangent function value.

``````public class CustomMath {

static double calculateAngle(double a, double b) {
return Math.atan(a / b);
}

public static void main(String[] args) {
/*
|\
| \ h
a |  \
|__*\ <- angle
b
*/

double a, b;

// a an b build isosceles right triangle
a = 3;
b = a;
System.out.println( calculateAngle(a, b) ); // 0.7853981633974483 <- ~45 degrees

// a and b build half of equilateral triangle
a = 3;
b = a * Math.sqrt(3);
System.out.println( calculateAngle(a, b) ); // 0.5235987755982988 <- ~30 degrees

// a and b build very high (+Inf) and slim (~0) triangle
a = Double.POSITIVE_INFINITY;
b = 0;
System.out.println( calculateAngle(a, b) ); // 1.5707963267948966 <- ~90 degrees
}
}``````

## 1. Documentation

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

## 2. Working with degrees

``````public class CustomMath {

static double calculateAngle(double a, double b) {
double angle = Math.atan(a / b);

return (180 / Math.PI) * angle; // rad to deg conversion
}

public static void main(String[] args) {
/*
|\
| \ h
a |  \
|__*\ <- angle
b
*/

double a, b;

// a an b build isosceles right triangle
a = 3;
b = a;
System.out.println( calculateAngle(a, b) ); // ~45 degrees

// a and b build half of equilateral triangle
a = 3;
b = a * Math.sqrt(3);
System.out.println( calculateAngle(a, b) ); // ~30 degrees

// a and b build very high (+Inf) and slim (~0) triangle
a = Double.POSITIVE_INFINITY;
b = 0;
System.out.println( calculateAngle(a, b) ); // ~90 degrees
}
}``````

## References

1. Inverse trigonometric functions - Wikipedia

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