       Re: DSolving(?) for a given tangent

• To: mathgroup at smc.vnet.net
• Subject: [mg82504] Re: DSolving(?) for a given tangent
• From: Jerry <JLK2941 at yahoo.com>
• Date: Mon, 22 Oct 2007 05:44:50 -0400 (EDT)
• References: <fct9c4\$r6e\$1@smc.vnet.net> <fd2fmv\$s0e\$1@smc.vnet.net>

```Sir, for some reason this does not work on my XP machine
using V6. I get the correct answer if I use

In:= {x, f[x]} /. First[Quiet[Solve[D[f[x], x] == 1.0, x]]]

This gives {6.8824, 4.54545} for output.

I'm guessing your "Degree" is different from mine which is
0.0174533.

Regards, Jerry

> On Sep 20, 10:01 am, "AngleWyrm" <anglew... at yahoo.com> wrote:
>> Don't know for sure if this is the right function, so here's the scenario:
>>
>> f[x_] := E^(0.22 x);
>> Plot[f[x], {x, 6, 36}]
>>
>> Which plots a nice escalating curve.
>>
>> What I would like to know is: Where is the point {x,f[x]} that has a
>> 45-degree tangent line; ie where is this curve's balance point before it
>> really starts taking off?
>
> In:= f[x_] := E^(0.22*x);
> In:= {x, f[x]} /. First[Quiet[Solve[D[f[x], x] == 45*Degree, x]]]
>
> Out= {6.882398784680798, 4.545454545454546}
>
> Quiet suppresses the warning message:
> Solve::ifun:Inverse functions are being \
> used by Solve, so some solutions may not be found; use Reduce for \
> complete solution information. >>
>
> This verifies the result
> In:=  D[f[x], x]/Degree /.  First[Quiet[Solve[D[f[x], x] ==
> 45*Degree, x]]]
>
> Out= 45.
>