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MathGroup Archive 2004

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Re: Simplify stuck in simple expression

  • To: mathgroup at
  • Subject: [mg50164] Re: Simplify stuck in simple expression
  • From: carlos at (Carlos Felippa)
  • Date: Wed, 18 Aug 2004 01:20:18 -0400 (EDT)
  • References: <cfsi9a$a78$>
  • Sender: owner-wri-mathgroup at

Bob Hanlon <hanlonr at> wrote in message news:<cfsi9a$a78$1 at>...
> expr = (2-Sqrt[72*(1+a*b)^2+4])/(2*a);
> You can work around the problem by using a temporary change in variables 
> (x = a*b + 1)
> Simplify[expr /. b-> (x-1)/a] /. x->a*b+1
> or
> Simplify[expr /. a-> (x-1)/b] /. x->a*b+1 // Cancel
> Bob Hanlon
Unfortunately it isnt practical.  That expression is inside a deep
loop that solves thousands of quadratic equations, and the expressions
under Sqrt keep changing.   I just cooked up a simplified form for

Is there an equivalent of FactorTerms that can force a numerical
factor out of a symbolic square root?

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