How to find the area and circumference of a circle in javascript-JS Tutorial-php.cn

How to find the area and circumference of a circle in javascript

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Release： 2021-11-22 10:41:13

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Method to find the area and circumference of a circle: 1. Use the PI attribute of the Math object and the pow() method to calculate the area of the circle. The syntax is "Math.PI * Math.pow(radius, 2)" ;2. Use the PI attribute of the Math object to calculate the circumference of the circle. The syntax is "2 * Math.PI * radius".

How to find the area and circumference of a circle in javascript

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

How to find the area and circumference of a circle in JavaScript

You can use the Math object to implement mathematical operations in JavaScript, and the Math object is used to perform Math tasks.

Math object is not a class of objects like Date and String, so there is no constructor Math().

For example:

var x = Math.PI; // 返回PI
var y = Math.sqrt(16); // 返回16的平方根

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There is also the pow() method

The syntax is:

Math.pow(x,y)

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The pow() method returns x raised to the y power .

Let’s take a look at how to calculate the primary color area and perimeter based on an example. The example is as follows:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
    //四舍五入
    function round(number, X) {
        X = (!X ? 2 : X);
        return Math.round(number*Math.pow(10,X))/Math.pow(10,X);
        }
        var r = Number(prompt(&#39;请输入圆的半径&#39;));
        if(!isNaN(r)) {
            var m = round(Math.PI * Math.pow(r, 2), 2);
            var c = round(2 * Math.PI * r);
            alert(&#39;面积=&#39; + m + &#39;\n&#39; + &#39;周长=&#39; + c);
            } else {
                alert(&#39;请输入数字!&#39;);
                }
</script>
</body>
</html>

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Output result:

How to find the area and circumference of a circle in javascript

After the input radius is 5, the output result is:

How to find the area and circumference of a circle in javascript

[Recommended learning: javascript advanced tutorial]

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