How to find the area and circumference of a circle in javascript
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".
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
There is also the pow() method
The syntax is:
Math.pow(x,y)
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('请输入圆的半径'));
if(!isNaN(r)) {
var m = round(Math.PI * Math.pow(r, 2), 2);
var c = round(2 * Math.PI * r);
alert('面积=' + m + '\n' + '周长=' + c);
} else {
alert('请输入数字!');
}
</script>
</body>
</html>Output result:
After the input radius is 5, the output result is:
[Recommended learning: javascript advanced tutorial]
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