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What does this mean?

 Feb 19, 2019
 #1
avatar+18495 
+2

To have real coeeficients there has to be a    -  i    root also

 

Quadratic formula:

\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)      

     shows that to have an i root the discriminant has to be NEGATIVE...and the disriminant is a + or - term....so there will be ANOTHER -2i root to go with the +2 i root

 Feb 19, 2019
edited by ElectricPavlov  Feb 19, 2019
 #2
avatar+101872 
+3

To expand on EP's answer

 

If   a + bi    is a root of a polynomial......then so is  a - bi

 

These are known as "conjugate pairs"  

 

Thus....if we have complex roots of a polynomial, they will occur in pairs

 

So   the conjugate of  0 + 2i    is    0 - 2i

 

cool cool cool

 Feb 19, 2019
edited by CPhill  Feb 19, 2019

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