       Re: Problem with finding angles between points in Cartesian plane

• To: mathgroup at smc.vnet.net
• Subject: [mg26140] Re: Problem with finding angles between points in Cartesian plane
• Date: Tue, 28 Nov 2000 01:56:39 -0500 (EST)
• References: <8vfqv9\$jif@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Derek,

Try the alternate version of ArcTan, ArcTan[x,y].  See Help under
ArcTan.

In:=
x1 = 3;
y1 = 4;
x2 = 3;
y2 = 6;
(180/Pi)*ArcTan[(x2 - x1), (y2 - y1)]
(180/Pi)*ArcTan[(x1 - x2), (y1 - y2)]

Out=
90

Out=
-90

In article <8vfqv9\$jif at smc.vnet.net>,
"Blitzer" <drek1976 at yahoo.com> 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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