JavaScript acos: How to Use Math.acos() Function

The acos() method comes in handy in programming contexts dealing with any trigonometric expressions. The acos() is a static method of Math, and it can be used without creating an object.

JavaScript Math acos

The Math.acos() is a built-in JavaScript function that is used to find the arccosine value of a given argument. To find an arccosine value of a given argument in JavaScript, use the Math.acos() method.

The Math.acos() function is used to return the arccosine of a number in radians. The Math.acos() method returns the numeric value between 0 and pi radians.

Syntax

Math.acos(x)

Parameter(s)

The variable x lies between -1 and 1 whose arccosine value is to be determined.

Return Value

The arccosine value is between 0 and pi radians.

See the following figure.

Note:

• If the passed value lies outside the range [-1,1], the method returns NaN.

Compatibility

• Google Chrome
• Internet Explorer
• Firefox
• Opera
• Safari
• Android webview
• Chrome for Android
• Firefox for Android
• Opera for Android
• Safari on iOS
• Samsung Internet
• Node.js

JavaScript version: ECMAScript 1

Consider the following examples.

JavaScript Math acos() Code Example

The following example demonstrates the use of the Javascript Math acos() method.

// example1.js

var a = -1;
var b = 1;
var c = 0.5;
var d = 0;

console.log(Math.acos(a));
console.log(Math.acos(b));
console.log(Math.acos(c));
console.log(Math.acos(d));

Output

node example1
3.141592653589793
0
1.0471975511965979
1.5707963267948966

Example 2

The following example demonstrates the case where values outside the range of [-1,1] are passed as parameters.

// example2.js

var a = 2;
var b = -2;

console.log(Math.acos(a));
console.log(Math.acos(b));

Output

node example2
NaN
NaN

Example 3

The following example demonstrates an application of this method in a simple programming context.

Given the three sides of a right-angled triangle, find all of its angles.

// example3.js

var h;
var b;
var p;

const r = require('readline');
const rl = r.createInterface({
  input: process.stdin,
  output: process.stdout
});

const prompt1 = () => {
  return new Promise((resolve, reject) => {
    rl.question('Hypotenuse: ', (answer) => {
      h = answer;
      resolve();
    });
  });
};

const prompt2 = () => {
  return new Promise((resolve, reject) => {
    rl.question('Base: ', (answer) => {
      b = answer;
      resolve();
    });
  });
};

const prompt3 = () => {
  return new Promise((resolve, reject) => {
    rl.question('Perpendicular: ', (answer) => {
      p = answer;
      resolve();
    });
  });
};

const main = async () => {
  await prompt1();
  await prompt2();
  await prompt3();
  rl.close();

  console.log('The three angles of the triangle are(in radians):');
  console.log(Math.acos(0));		 		//pi/2 radians
  console.log(Math.acos(b / h)); 			//base angle
  console.log(Math.acos(0) - Math.acos(b / h)); 	//third angle
}

main();

Output

Test Case 1:
->node example3
Hypotenuse: 6.928
Base: 6
Perpendicular: 3.464
The three angles of the triangle are:
1.5707963267948966
0.523547964303085
1.0472483624918114

Test Case2:
->node example3
Hypotenuse: 42.426
Base: 30
Perpendicular: 30
The three angles of the triangle are(in radians):
1.5707963267948966
0.7853885732135081
0.7854077535813885

See also

JavaScript Math asin()

Javascript Math asinh()

JavaScript Math atan()

JavaScript Math atanh()

JavaScript Math atan2()

Javascript math cos()

Javascript math.cosh()

Javascript Math.abs()

Javascript Math.round()

Javascript Math.random()