       Re: Problem with finding angles between points in Cartesian plane

• To: mathgroup at smc.vnet.net
• Subject: [mg26090] Re: Problem with finding angles between points in Cartesian plane
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Tue, 28 Nov 2000 01:55:35 -0500 (EST)
• References: <8vfqv9\$jif@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Derek,
We can use the two-entry (vector?) form:

?ArcTan

"ArcTan[z] gives the arc tangent of the complex number z. ArcTan[x, y] gives
\
the arc tangent of y/x, taking into account which quadrant the point (x, y)
\
is in."

Thus:

ArcTan[0, 3]

Pi/2

--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Blitzer" <drek1976 at yahoo.com> wrote in message
news:8vfqv9\$jif at smc.vnet.net...
> 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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