sqrt

(PHP 4, PHP 5, PHP 7)

sqrt — 平方根

说明

float sqrt ( float $arg )

返回 arg 的平方根。

参数

arg: 要处理的参数

返回值

返回 arg 的平方根，负数时返回 NAN。

范例

Example #1 sqrt() 例子


<?php
// Precision depends on your precision directive
echo sqrt(9); // 3
echo sqrt(10); // 3.16227766 ...
?>

参见

pow() - 指数表达式

User Contributed Notes

justin at hoogs dot com dot au 10-Mar-2015 01:12


As we all know, the square of the hypotenuse is equal to the sum of the squares of the other two sides of a right triangle (a2 + b2 = c2).



With that in mind I created a quick way to reduce images to a maximum area without messing up width/height constraints.



<?php

list($width_orig, $height_orig) = getimagesize($img);



$max_a = 500000; // maximum area in pixels



$width = $width_orig;

$height = $height_orig;



$area = $width * $height;

if ($area > $max_a) { 

    $mult = sqrt($max_a) / sqrt($height * $width);

    $width *= $mult;

    $height *= $mult;

}

?>

jouhni at web dot de 17-Feb-2005 08:46


To get any root of a number your can use the pow() function:



pow(8, 1/3)



which gives you the third root of eight.



Jouhni