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這個方法返回一個數的平方根。如果數的值是負的，開方返回NaN。
文法
Math.sqrt( x ) ;
下面是參數的詳細資料：
傳回值:
例子：
<html><head><title>JavaScript Math sqrt() Method</title></head><body><script type="text/javascript">var value = Math.sqrt( 0.5 );document.write("First Test Value : " + value ); var value = Math.sqrt( 81 );document.write("<br />Second Test Value : " + value ); var value = Math.sqrt( 13 );document.write("<br />Third Test Value : " + value ); var value = Math.sqrt( -4 );document.write("<br />Fourth Test Value : " + value ); </script></body></html>
這將產生以下結果：
First Test Value : 0.7071067811865476Second Test Value : 9Third Test Value : 3.605551275463989Fourth Test Value : NaN
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