How to calculate the area and perimeter of a circle by javascript
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The method of calculating the circle area and perimeter: 1, using 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, using the PI attribute of the Math object to calculate the perimeter of the circle, the syntax is "2 * Math.PI * radius".
The operating environment of this tutorial: windows7 system, javascript1.8.5 version, Dell G3 computer.
How to find the area and perimeter of a circle by javascript
You can use the Math object in JavaScript to perform mathematical operations, and the Math object is used to perform mathematical tasks.
The Math object is not a class of objects like Date and String, so there is no constructor Math ().
For example:
Var x = Math.PI; / / returns PIvar y = Math.sqrt (16); / / returns the square root of 16
There is also the pow () method
The syntax is:
Math.pow (XBI y)
The pow () method returns the y power of x.
Let's take a look at how to calculate the primary color area and perimeter based on an example, as follows:
Document / / rounding function round (number, X) {X = (! X? 2: X); return Math.round (number*Math.pow (10Magine X)) / Math.pow (10Magazine X);} var r = Number (prompt ('Please enter the radius of the circle')) If (! isNaN (r)) {var m = round (Math.PI * Math.pow (r, 2), 2); var c = round (2 * Math.PI * r); alert ('area =' + m +'\ n' + 'perimeter =' + c);} else {alert ('Please enter a number!');}
Output result:
After the input radius is 5, the output result:
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