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If $x + y =2$ and $xy = 23$, then what is $x^2 + y^2$?

 Oct 1, 2017
 #1
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If $x + y =2$ and $xy = 23$, then what is $x^2 + y^2$?

 

x + y  = 2    square both sides

 

x^2 + 2xy + y^2  =  4

 

x^2 + 2(23) + y^2  = 4

 

x^2 + 46  +  y^2   =  4     subtract 46 from both sides

 

x^2  + y^2  =  -42

 

Thanks to the guest for spotting my error !!!

 

 

  

 

CPhill Sep 29, 2017

 Oct 1, 2017
edited by CPhill  Oct 1, 2017
 #2
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Just saying 4-46= -42 not -44.

 Oct 1, 2017

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