Java Math acos() Method

The Math.acos() method returns the arc cosine of an angle between 0.0 and pi (0.0, pi). Arc cosine is also called as inverse of a cosine. If the argument is NaN or its absolute value is greater than 1, then the result is NaN.

Syntax of Math acos() Method

public static double acos(double a)

• Parameter: a: The value whose arc cosine is to be returned.
• Return: This method returns the arc cosine of the argument.

Important Points:

• Our input should be only between -1.0 and 1.0. The values outside this range will result in NaN.
• If |a| > 1 or a is NaN, the method returns NaN.
• Any value whose absolute value exceeds 1, results NaN.

Examples of Java Math acos() Method

Example 1: Input Outside [-1, 1]

NaN

Explanation: In this example, Math.PI i.e., ~3.14 is outside the valid domain so the result is NaN.

Example 2: Convert Degrees to Radians

1.5159376794536454

Example 3: Different Valid and Invalid Inputs

acos(1.0) = 0.0
acos(0.0) = 1.5707963267948966
acos(-1.0) = 3.141592653589793
acos(1.5) = NaN

This method is useful in trigonometric calculations when we need the angle whose cosine is a given value.