       Re: Perpendicular lines do not appear perpendicular

• To: mathgroup at smc.vnet.net
• Subject: [mg100337] Re: Perpendicular lines do not appear perpendicular
• From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
• Date: Mon, 1 Jun 2009 07:09:22 -0400 (EDT)
• References: <gvtmhv\$gh8\$1@smc.vnet.net>

```Hi Bill,

It looks perfectly perpendicular on my screen. Could you check the
resolution to which your monitor is set? It might be that you have set
it to a non native resolution with an aspect-ratio that's not 16:10
(which would be natural for your screen).

Cheers -- Sjoerd

On May 31, 12:35 pm, Bill <WDWNORW... at aol.com> wrote:
> Perpendicular lines do not appear perpendicular
>
> Hi:
>
> I have taken the line equation 2*x+4*y-6==0, and rotated it 90 degree=
> using a 3x3 rotation matrix.
> Here's the Mathematica 6.0.1 code that I used:
>
> rMat = {{Cos[90 Degree], - Sin[90 Degree], 0}, {Sin[90 Degree],
> Cos[90 Degree], 0}, {0, 0, 1}}
>
> l={2, 4, -6}
>
> rMat.l
>
> Output: {-4,2,-6}
>
> Placing these numbers into the general form of the equation of the line A=
x+By+c=0, I get -4*x + 2*y - 6 == 0.
> Placing the 2 perpendicular line equations into ContourPlot:
>
> ContourPlot[{2*x + 4*y - 6 == 0, -4*x + 2*y - 6 == 0}, {x, -4,
>   4}, {y, -4, 4}, AspectRatio -> 1]
>
> and plotting, I notice that on my pc screen that the lines do not look pe=
rpendicular, as does the plot frame.
> Perhaps this is just my computer screen, a HP f2105. I can hold up a squa=
re cut piece of paper to the lines
> on the screen, and notice the out-of-square condition. I used AspectRatio=
->1, but still no joy.
>
> Question: Can someone suggest a remedy for my problem, if one exists?
>