How to use the Law of Cosines In Javascript

Using the Law of Sines

In this approach, first we will find the length of each side using vertices, then we will calculate the alpha beta gamma angles of triangles using the cosine of trigonometry, and we will find the cosine through Math.acos() method.

Syntax:

let xDiff = point1[0] - point2[0];
let yDiff = point1[1] - point2[1];
return xDiff * xDiff + yDiff * yDiff;

Javascript

// JavaScript program to find all three angles 
// of a triangle given coordinate of all three  
// vertices 
  
// Returns square of distance b/w two points 
function lengthSquare(X, Y) { 
    let xDiff = X[0] - Y[0]; 
    let yDiff = X[1] - Y[1]; 
    return ( 
        xDiff * xDiff + yDiff * yDiff 
    ); 
} 
  
const calculateAngle = ( 
    vertices1, 
    vertices2, 
    vertices3 
) => { 
  
    // Square of lengths be a2, b2, c2 
    let a2 = lengthSquare( 
        vertices2, 
        vertices3 
    ); 
    let b2 = lengthSquare( 
        vertices1, 
        vertices3 
    ); 
    let c2 = lengthSquare( 
        vertices1, 
        vertices2 
    ); 
  
    // Length of sides be a, b, c 
    let a = Math.sqrt(a2); 
    let b = Math.sqrt(b2); 
    let c = Math.sqrt(c2); 
  
    // From Cosine law 
    let alpha = Math.acos( 
        (b2 + c2 - a2) / (2 * b * c) 
    ); 
      
    let beta = Math.acos( 
        (a2 + c2 - b2) / (2 * a * c) 
    ); 
    let gamma = Math.acos( 
        (a2 + b2 - c2) / (2 * a * b) 
    ); 
  
    // Converting to degree 
    alpha = (alpha * 180) / Math.PI; 
    beta = (beta * 180) / Math.PI; 
    gamma = (gamma * 180) / Math.PI; 
  
    // Printing all the angles 
    console.log("alpha : ", alpha); 
    console.log("beta : ", beta); 
    console.log("gamma : ", gamma); 
}; 
  
// Driver code 
let vertices1 = [0, 0]; 
let vertices2 = [0, 5]; 
let vertices3 = [5, 0]; 
  
calculateAngle( 
    vertices1, 
    vertices2, 
    vertices3 
);

Output

alpha :  90
beta :  45.00000000000001
gamma :  45.00000000000001

JavaScript Program to Find All Angles of a Triangle

In this article, we are going to implement a program through which we can calculate each angle of a triangle by its vertices. We will input the vertices of the triangle and return the angle to the main program.

Examples:

Input : Vertex A = (0, 5), 
            Vertex B = (0, 0), 
            Vertex C = (5, 0)
Output : 90, 45, 45

All possible approaches to find the angle.

Table of Content

Using the Law of Cosines
Using the Law of Sines

Tags:

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Using the Law of Sines

How to use the Law of Cosines In Javascript

Javascript

JavaScript Program to Find All Angles of a Triangle

Table of Content

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