       Re: Problem with finding angles between points in Cartesian plane

• To: mathgroup at smc.vnet.net
• Subject: [mg26101] Re: [mg26060] Problem with finding angles between points in Cartesian plane
• From: Carl Woll <carlw at u.washington.edu>
• Date: Tue, 28 Nov 2000 01:55:44 -0500 (EST)
• References: <200011220655.BAA19930@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Try using the two argument version of ArcTan, e.g.

ArcTan[x1-x1,y2-y1]

will do the trick.

Carl Woll
Physics Dept
U of Washington

Blitzer wrote:

> I would like to find the angle between 2 points on the Cartesian plane.
> However, if I use "ArcTan", it is not able to recognise that points with the
> same x-coordinates have an angle of 90 degrees between them. It returns
> "Indeterminate".
> eg. for a point A (x1, y1) and a point (x1, y2), to find the angle between
> them, I use ArcTan[(y2-y1)/(x1-x1)]. However, as the denominator is equal to
> "0", this function returns "indeterminate". Is there a way to get around
> this problem? Or is there other possible functions which can be used.
> I am dealing with a very large array of numbers and thus, it's not possible
> to check the coordinates individually.
>
> Would be grateful for any help rendered. Thanks!
>
> Derek

```

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