       Re: How can I obtain the common tangent of two curves within

• To: mathgroup at smc.vnet.net
• Subject: [mg114932] Re: How can I obtain the common tangent of two curves within
• From: Peter Breitfeld <phbrf at t-online.de>
• Date: Thu, 23 Dec 2010 03:53:48 -0500 (EST)
• References: <ies9uk\$aak\$1@smc.vnet.net>

```Hongyi Zhao wrote:

> Dear all,
>
> I've two curves corresponding to two functions, say, y=f_1(x),  and
> y=f_2(x).  Now, I want to obtain the common tangent of these two
> curves within mathematica? What code or commands I should use for this
>
> Best regards.
>

Suppose your common tangent is g[x_]=m x+c. Then you have to solve the
system of equations:

eqns= {f1[u]==g[u],f1'[u]==m,f2[v]==g[v],f2'[v]==m}

Now solve the system:

sol=Solve[eqns,{m,c,u,v}]

g[x_]=m x+c /.sol[]

--
_________________________________________________________________
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de

```

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