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Re: Cancel order

On 29 Nov 2011, at 13:05, =E9=81=93 =E5=8E=9A wrote:

> How can I make Sqrt[(v1^2+v2^2)(g^2+gp^2)]/Sqrt[v1^2+v2^2] simple in
> mathematica?

You need the assumption that the expressions under the square root are positive. So:

Assuming[g^2 + gp^2 >= 0 && v1^2 + v2^2 > 0,
   Simplify[Sqrt[(g^2 + gp^2)*(v1^2 + v2^2)]/Sqrt[v1^2 + v2^2]]]

Sqrt[g^2 + gp^2]

In particular, this will be true if everything in your expression is real:

Assuming[Element[_, Reals],
   Simplify[Sqrt[(g^2 + gp^2)*(v1^2 + v2^2)]/
       Sqrt[v1^2 + v2^2]]]

Sqrt[g^2 + gp^2]

Andrzej Kozlowski

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