Re: Manipulate help

• To: mathgroup at smc.vnet.net
• Subject: [mg128592] Re: Manipulate help
• From: "Nasser M. Abbasi" <nma at 12000.org>
• Date: Thu, 8 Nov 2012 02:08:46 -0500 (EST)
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• References: <k7ct9k\$dqn\$1@smc.vnet.net>

```On 11/6/2012 11:58 PM, 07.350z wrote:
> Create a Manipulate demonstration that draws the tangent line to a curve at the point
>specified by a continuous control. For the curve, the user should be able to
>choose between the graphs of the following functions. Make sure your demonstration
>shows the curve, the point, and the tangent line at that point. The functions are 7cos(x),
> x^2/10, 2ln(1+x^2)
>
> Show[Manipulate[
>    Plot[y, {x, -10, 10},
>     PlotRange -> {-10, 10}], {y, {7 Cos[x], x^2/10, 2*Log[1 + x^2]}}],
>   Do[Module[{slopeM, tangentLine, x},
>     slopeM = D[{7 Cos[x], x^2/10, 2*Log[1 + x^2]}, x] /. x -> t;
>     tangentLine = slopeM*x - t;
>     Return[
>      Plot[{{7 Cos[x], x^2/10, 2*Log[1 + x^2]}, tangentLine}, {t, -5,
>        5}]]], {x, -10, 10}]]
>
> I know the first part of code is right, but I'm having trouble adding the tangent line.
>Any help would be great thanks!
>

may be

-------------------------------------------
Manipulate[
Module[{lineEquation, pt = {at, y /. x -> at}},
lineEquation = getSlope[at, y, x];
Plot[{y, lineEquation }, {x, -10, 10}, PlotRange -> {-10, 10},
Epilog -> {Red, PointSize[.02], Point[pt]}]
],

{y, {7 Cos[x], x^2/10, 2*Log[1 + x^2]}},
{{at, 0, "x"}, -10, 10, 1, Appearance -> "Labeled"},
TrackedSymbols :> {y, at},

Initialization :>
(
getSlope[at_, y_, var_] := Module[{slope, h, intercept},
h = y /. var -> at;
slope = D[y, var] /. var -> at;
intercept = h - at*slope;
slope*var + intercept
]
)
]
----------------------------------

--Nasser

```

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