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

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

Just saying 4-46= -42 not -44.