If I have $q(x)=x_1^2-x_1x_2-x_1x_3+x_2x_3$
How do I find the maximum value of $q(x)$ subject to the constraint $||x||=4$?
I already know the max when $||x||=1$ since it is the eigenvalue, but I don't know about when it is higher than $1$.
Also, how do I draw the plot of $q(x)=3$ ? I have $q(x)=x^T\cdot <<1,0,0>|<-1,0,1>|<-1,0,0>> \cdot x$ and I know I need to find $P$, but the eigenvectors I've found $(<1,0,0>$ and $<1,1,0>)$ are not orthogonal.
Thanks very much for the help