- #1
talolard
- 125
- 0
Homework Statement
For what real values of the parameters a,b,c,d does the functiob [tex] f(x,y)=ax^3+by^3+cx^4+dy^4-(x+y)^5 [/tex] have a local minimum at (0,0)
Homework Equations
I calculated the gradient at (0,0) and it is always zero regardless of parameters.
The problem is that the Hessian matrix is also zero so I don't know what kind of criticial point it is.
I also noticed that if (0,0) is a minimum then [tex] ax^3+by^3+cx^4+dy^4>(x+y)^5 [/tex] in the nieberhood but that still hasnt taken me very far.
I don't see how I can use Lagrange multipliers, the inverse or implicit function theorems, since the gradient is 0 which precludes using them in any direct way. So my arsenal seems rather depleted.
Any ideas?
Thanks
Tal