Re: How can draw Focus(Points)
- To: mathgroup at smc.vnet.net
- Subject: [mg17151] Re: [mg17139] How can draw Focus(Points)
- From: Manuel Arala Chaves <machaves at fc.up.pt>
- Date: Sun, 18 Apr 1999 00:59:40 -0400
- Sender: owner-wri-mathgroup at wolfram.com
On Sat, 17 Apr 1999, Clara wrote:
> Hello
>
> I am beginner in Mathematica. I have created the parabola using:
> Plot1= Plot[ {y = 1/2x^2, y = -4}, {x, -4, 4},
> AxesLabel -> {"xx","yy"}
> , PlotStyle -> Hue[160/255],
> AxesStyle -> Hue [160/255] ]
>
> Now I want put the focus (point) in graphics. How can I do? Please help
> me.
>
>
>
You may add:
Focus=Graphics[{PointSize[.02],Hue[160/255],Point[{0,.5}]}];
Show[Plot1,Focus, AspectRatio->Automatic]
But if your line under the parabola is supposed to be the directrix, there
is a mistake; the following will draw the parabola plus both focus and
directrix:
Plot2= Plot[ {0.5 x^2, -0.5}, {x, -4, 4}, AxesLabel -> {"xx","yy"},
PlotStyle -> Hue[160/255], AxesStyle -> Hue [160/255],
DisplayFunction->Identity ];
Focus=Graphics[{PointSize[.02],Hue[160/255],Point[{0,.5}]}];
Show[Plot2,Focus, AspectRatio->Automatic,
DisplayFunction->$DisplayFunction]
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