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MathGroup Archive 1998

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Re: Integrate lesson




Will Self wrote:
|
|Hi Ted,
|
|expr=Sqrt[2] x - (Sqrt[2]+Sqrt[3])x^x+Sqrt[5+2Sqrt[6]]x^x; |
|FullSimplify[expr]
|
|My results varied from yours.  There is no way that FullSimplify |is
going to get rid of that x^x.
|

I am using Version 3.0.1.
FullSimplify[expr]  gives me   Sqrt[2]*x. You say there is no way
FullSimplify is going to get rid of that x^x. Well it can be done with
the steps below:

expr=Sqrt[2] x - (Sqrt[2]+Sqrt[3])x^x+Sqrt[5+2*Sqrt[6]]x^x

    Factor (x^x) out of two terms.

expr= Sqrt[2] x + (  -(Sqrt[2]+Sqrt[3])+Sqrt[5+2*Sqrt[6]]  )x^x;

    For readability let:   u=Sqrt[2]+Sqrt[3]

expr==Sqrt[2] x + (-u+Sqrt[5+2*Sqrt[6]])x^x

expr==Sqrt[2] x + (-Sqrt[u^2]+Sqrt[5+2*Sqrt[6]])x^x

       u^2=(Sqrt[2]+Sqrt[3])^2
       u^2=2+2*Sqrt[2]*Sqrt[3]+ 3
       u^2=5+2 Sqrt[6]

expr=Sqrt[2] x + ( -Sqrt[5+2 Sqrt[6]] +Sqrt[5+2 Sqrt[6]] )x^x

expr=Sqrt[2] x + (0) x^x

expr=Sqrt[2] x


I will not jump on the band wagon with those who want to complain that 
Integrate, DSolve, Solve etc. aren't smart enough.  These people want a
few  commands that can solve any problem.  Solutions would take much
longer if  every expression went through FullSimplify (or other
changes) before trying  to solve the problems.

The better approach is to simplify the expression with Together, Expand,
Factor, TrigExpand, FunctionExpand, ComplexExpand, etc.  WITH human 
intelligence.  After all that a user can use Simplify  (or in some
cases use  FullSimplify).

Ted Ersek




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