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Re: Thread function now working as expected
*To*: mathgroup at smc.vnet.net
*Subject*: [mg74612] Re: [mg74587] Thread function now working as expected
*From*: Bob Hanlon <hanlonr at cox.net>
*Date*: Wed, 28 Mar 2007 01:43:26 -0500 (EST)
*Reply-to*: hanlonr at cox.net
eqn1 = Sqrt[1+196*x^4] == 12*x-1-14*x^2;
To square both sides of an equation just use Map (/@)
eqn2 = #^2& /@ eqn1
196*x^4 + 1 == (-14*x^2 + 12*x - 1)^2
To expand both sides of an equation use ExpandAll
eqn3 = eqn2//ExpandAll
196*x^4 + 1 == 196*x^4 - 336*x^3 + 172*x^2 - 24*x + 1
eqn3//Simplify
x*(84*x^2 - 43*x + 6) == 0
However, you do not need to expand eqn2 to get this result
eqn2//Simplify
x*(84*x^2 - 43*x + 6) == 0
Bob Hanlon
---- siewsk at bp.com wrote:
> I cannot get the Thread function to work on In[3] and I
> am forced to do it manually in In[4]
>
> Does anyone has any idea why In[3] is not working as I expected?
>
> In[1]:= eqn1 = Sqrt[1 + 196*x^4] == 12*x - 1 - 14*x^2
> Out[1]=
> 4 2
> Sqrt[1 + 196 x ] == -1 + 12 x - 14 x
>
>
> In[2]:= eqn2 = Thread[(#1^2 & )[eqn1], Equal]
> Out[2]=
> 4 2 2
> 1 + 196 x == (-1 + 12 x - 14 x )
>
>
> In[3]:= dummy = Thread[Expand[eqn2], Equal]
> Out[3]=
> 4 2 2
> 1 + 196 x == (-1 + 12 x - 14 x )
>
>
> In[4]:= eqn3 = Equal[ eqn2[[1]] , Expand[ eqn2[[2]] ] ]
> Out[4]=
> 4 2 3 4
> 1 + 196 x == 1 - 24 x + 172 x - 336 x + 196 x
>
>
> In[5]:= Simplify[eqn3]
> Out[5]=
> 2
> x (6 - 43 x + 84 x ) == 0
>
>
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