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Homework Statement
Find critical points. [itex]f(x,y) = (x-1)^4 + (x-y)^4[/itex]
The Attempt at a Solution
[itex]\frac{\partial f}{\partial x} = 4(x-1)^3 + 4(x-y)^3 [/itex]
[itex]\frac{\partial f}{\partial y} = - 4(x-y)^3 [/itex]
[itex]\frac{\partial f}{\partial x} = 0 [/itex],
[itex]\frac{\partial f}{\partial y} = 0 [/itex],
[itex]- 4(x-y)^3 = 0 [/itex], x=y
[itex]4(y-1)^3 + 4(y-y)^3 = 0[/itex],
We have a critical point at: y=1,x=1
So as the both part of the function ( [itex](x-1)^4[/itex] and [itex](x-y)^4[/itex] ) will always be grater or equeal 0, and the critical point gives us 0, then I guess it's a min, no?
So if I'm not wrong, then why is inconclusive the second derivative text AC-B^2=0
A=Fxx, C=Fyy, B=Fxy
Thanks!