# Javascript Program to Find the Area of a Triangle

In this example, you will learn to write a javascript program to find the area of a triangle.

But before going into the example, you must have knowledge of the following JavaScript topics:

To find the area of a triangle we have two cases.

## Case 1

If the base and height of a triangle are known to you, you can find the area using the following formula:

area = (base * height) / 2

### Example 1: Area of Triangle When Base And Height are Known

``````const base = prompt('Enter the base of a triangle: ');
const height = prompt('Enter the height of a triangle: ');

//calculate the area
const area = (base * height) / 2;

console.log(`Area of the triangle is \${area}`);``````

Output

Enter the base of a triangle: 4
Enter the height of a triangle: 7
Area of the triangle is 14

## Case 2

If the length of the 3 sides is known to you, you can find the area using Heron’s formula.

s = (a+b+c)/2
area = √(s(s-a)(s-b)(s-c))

Here, `a`, `b` and `c` are the 3 sides of the triangle

### Example 2: Area of Triangle When All Sides are Known

``````const side1 = parseInt(prompt('Enter the length of side1: '));
const side2 = parseInt(prompt('Enter the length of side2: '));
const side3 = parseInt(prompt('Enter the length of side3: '));

//calculate the semi-perimeter
const s = (side1 + side2 + side3) / 2
//calculate the area
const area = Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));

console.log(`Area of the triangle is \${area}`);``````

Output

Enter the length of side1: 3
Enter the length of side2: 4
Enter the length of side3: 5
Area of the triangle is 6

Here, we have used `Math.sqrt()` to find the square root of the number.

### Example 3: Area of an Equilateral Triangle

An equilateral triangle is a triangle whose sides are equal, you can find the area of an equilateral triangle using the formula :

area = (√3)/4 × side2

``````const side = parseInt(prompt('Enter the length of the side: '));

//calculate the area
const area = (1.73 * side * side) / 4

console.log(`Area of the triangle is \${area}`);``````

Output

Enter the length of the side: 5
Area of the triangle is 10.8125