Take the 2-minute tour ×
Mathematica Stack Exchange is a question and answer site for users of Mathematica. It's 100% free, no registration required.

I want to check when the expression

$$ \sqrt{\sqrt{\lambda^{2}\left(2E+\lambda^{2}\right)}+E+\lambda^{2}} $$

is real, when it is purely imaginary and when it is complex (with imaginary part not zero).

Also I would like to know the sign of the imaginary part in the case it is non-zero. To check the last part, after some steps, I am using Reduce for inequalities like $\mathrm{Im}\left(\sqrt{\lambda^{2}\left(2E+\lambda^{2}\right)}\right)>0 $ but this is taking a lot of time on Mathematica. Is there a way to get the kind of results that I want more quickly?

The variables are real and the code I ran is

  Reduce[ Im[ Sqrt[ e + λ^2  -Sqrt[ λ^2 (2 e + λ^2)]]] > 0, {e, λ}]
share|improve this question
Can you include the code which is taking a long time? –  Jonathan Shock Jul 16 '13 at 17:11
Are the variables real ? –  b.gatessucks Jul 16 '13 at 17:16
Reduce[Im[Sqrt[e + x^2 + Sqrt[(x^2) (2*e + x^2)]]] == 0, x, Reals] for real vars –  belisarius Jul 16 '13 at 17:55
@belisarius Interestingly, Reduce doesn't seem to solve the <0 case correctly. –  Sjoerd C. de Vries Jul 16 '13 at 20:29

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.