# A Lengthy Foe

Calculus Level 3

$f(x,y,z,w)= x^2+9y^2+4z^2+w^2-6xy+4xz-2xw-12yz+6yw-4zw+x-3y+2z+w$

Find the (global) minimum of $$f(x,y,z,w)$$.

Enter 666 if you come to the conclusion that no such minimum exists.

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