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If the two roots of the quadratic 4x^2 + 7x + k are (-7 +/- i*sqrt(79))/8, what is k?

 Nov 29, 2020
 #1
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4x^2  +  7x  +  k

 

By Vieta's Theorem :

 

Product of the  roots  = k/4   ....so....

 

(-7 + i sqrt (79) )           (-7 - i sqrt (79) )

_____________   *   ______________   =

           8                               8

 

49 - 79i^2

________   =

      64

 

49 - 79 (-1)

__________  =

       64

 

49  +  79

________  =

      64

 

128

____  =    2

 64

 

 

And this =   k/4

 

So.....

 

k =  8

 

 

cool cool cool

 Nov 29, 2020

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