Re: How to find one expression in terms of another expression?

• To: mathgroup at smc.vnet.net
• Subject: [mg119765] Re: How to find one expression in terms of another expression?
• From: Jacare Omoplata <walkeystalkey at gmail.com>
• Date: Tue, 21 Jun 2011 05:52:21 -0400 (EDT)
• References: <itm0of\$143\$1@smc.vnet.net> <itolk6\$er6\$1@smc.vnet.net>

```Thanks for this answer.

On Jun 20, 7:37 pm, Ray Koopman <koop... at sfu.ca> wrote:
>
> Omit 'dt = t2 - t1'. Otherwise, every time you write 'dt'
> it will be replaced by 't2 - t1'. Here is all you need:
>
> In[1]:=
> T1 = (t1 - ((u x1)/c^2))/Sqrt[1 - (u^2/c^2)];
> T2 = (t2 - ((u x2)/c^2))/Sqrt[1 - (u^2/c^2)];
> dT = Simplify[T2 - T1] /. t2 - t1 -> dt
> {b,a} = CoefficientList[dT,dt]
>
> Out[3]= (c^2*dt + u*(x1 - x2))/(c^2*Sqrt[1 - u^2/c^2])
>
> Out[4]= {(u*(x1 - x2))/(c^2*Sqrt[1 - u^2/c^2]), 1/Sqrt[1 - u^2/c^2]}

```

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