How to find a real positive root of a bi-quadratic equation

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Suppose a bi-quadratic equation x^4+4*x^2-7=0. How to find a positive real root of it.
solve(x^4+4*x^2-7=0, x, Real, Positive)
Is the above correct?
How to use fsolve here?

Answers (1)

Matt J
Matt J on 15 Apr 2013
Edited: Matt J on 15 Apr 2013
Why not just use ROOTS?
>> roots([1 0 4 -7])
ans =
-0.6277 + 2.2764i
-0.6277 - 2.2764i

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