I'm having some trouble understanding the conclusions drawn in the second of these two slides.
Knipsel8.PNG
© Rijksuniversiteit Groningen
Knipsel9.PNG
© Rijksuniversiteit Groningen
I can see that both X 1 and X 2 cannot be 0 given the equations.
However, I don't understand how they came to X 1 2 = X 2 2
Also I do see that the four critical points hold, but again I don't know how they came to these points.
Is that simply something you should be able to see or is it also possible to determine them by computation.
Is there someone who can help me with this?
+2353 
