Question about Casio CFX-9850G Plus Calculator

# In complex number mode, how to get out?

Hi, I ws playing around with my calculator and Ive put it in a complex number mode.
When I try to solve a cubic equation, all of the solutions are in complex numbers, when they shouldnt be.

Thanks

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### k24674

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• Casio Master

You are making an assumption that is unwarranted.Namely that a cubic equation must necessarily have 3 real roots. This is not the case. If coefficients are complex you should expect some complex roots. Right?
If the coefficients are REAL then depending on the discriminant you can have three cases
DELTA positive : three distinct real roots
DELTA=0 , the equation has a multiple root and all roots are REAL
DELTA negative: the equation has ONE real root and 2 complex roots that are complex conjugate of each other.

It suffices to look at the Tartaglia/Cardano expressions of the roots to know that more often than not there iIn complex number mode, how to get out? - d64abc4.jpgbe complex roots. Posted on Jul 25, 2010

• k24674 Jul 25, 2010

Sorry here is the equation and its discriminant  ×

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