atan2 (y, x) returns the angle θ between the positive x -axis and the ray from the origin to the point (x, y), confined to (−π, π]. In computing and mathematics, the function atan2 is the 2- argument arctangent.

ATAN2 (y, x) returns the arc tangent of the two numbers x and y. It is similar to calculating the arc tangent of y / x, except that the signs of both arguments are used to determine the quadrant of the result. The result is an angle expressed in radians. To convert from radians to degrees, use the DEGREES function.

The calculator displays atan2 function result in degrees, radians and graphically.

单位圆内的atan2取值 旁边的图片显示内容是：在一个单位圆内 atan2 {\displaystyle \operatorname {atan2} } 函数在各点的取值。 圆内标注代表各点的取值的幅度表示。

atan2(a,b)是4象限反正切，它的取值不仅取决于a/b的atan值，还取决于点 (b, a) 落入哪个象限. 当点(b, a) 落入第一象限时，atan2(a,b)的范围是 0 ~ pi/2; 当点(b, a) 落入第二象限时，atan2(a,b)的范围是 pi/2 ~ pi; 当点(b, a) 落入第三象限时，atan2(a,b)的范围是 - pi～- pi/2;

The four-quadrant inverse tangent, atan2(Y,X), returns values in the closed interval [–π, π] based on the values of Y and X, as shown in the graphic. In contrast, atan(Y/X) returns results that are limited to the interval [–π/2, π/2], shown on the right side of the diagram.

\text{atan2} 的作用就是扩展到 [-\pi, \pi] ，即四个象限都可，具体的公式转换如下： 如果 x>0 ，那么本身就是一、四象限的点了，直接和 \text{atan} 等价 如果 x < 0 , 那么就是二、三象限了，根据 y 的范围来确定是哪个象限

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atan2 is based on the arctangent function, but it expects two arguments to correctly determine the resulting quadrant. The calculator gives an angle between positive axis x and the ray to the given point from point 0. The result corresponds to atan2 function, implemented in many computer languages and math libraries.

atan2 (y, x) returns the angle θ between the positive x -axis and the ray from the origin to the point (x, y), confined to (−π, π]. The function first appeared in the programming language Fortran in 1961. It was originally intended to return a correct and unambiguous value for the angle in converting from Cartesian coordinates to polar coordinates.