Definition and Usage
定义和用法

The atan() function returns the arctangent of a number as a numeric value between -PI/2 and PI/2 radians.
atan()函数的作用是：返回一个指定数值参数的反正切值。

The atan2() function returns the angle theta of an (x,y) point as a numeric value between -PI and PI radians.
atan2()函数的作用是：返回两个指定数值参数的反正切值。

Syntax
语法

atan(x)

atan2(x,y)

Example 1 - atan()
案例1 - atan()

The following example returns the arctangent of different numbers with the atan() function:
下面的案例将通过atan()返回不同数值参数所对应的反正切值：

<?php
echo(atan(0.50) . "<br />");
echo(atan(-0.50) . "<br />");
echo(atan(5) . "<br />");
echo(atan(10) . "<br />");
echo(atan(-5) . "<br />");
echo(atan(-10))
?>

The output of the code above will be:
上述代码将输出下面的结果：

0.463647609001
-0.463647609001
1.37340076695
1.4711276743
-1.37340076695
-1.4711276743

Example 2 - atan2()
案例2 – atan2()

The following example returns the angle theta of different (x,y) points with the atan2() function:
下面的案例将通过atan2()返回两个参数的反正切值：

<?php
echo(atan2(0.50,0.50) . "<br />");
echo(atan2(-0.50,-0.50) . "<br />");
echo(atan2(5,5) . "<br />");
echo(atan2(10,20) . "<br />");
echo(atan2(-5,-5) . "<br />");
echo(atan2(-10,10))
?>

The output of the code above will be:
上述代码将输出下面的结果：

0.785398163397
-2.35619449019
0.785398163397
0.463647609001
-2.35619449019
-0.785398163397

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