• May 7th 2012, 12:28 PM
monomoco
1) f(x,y) = 0 unless x>0 and $x^2 < y < 3x^2$
2) for each x > 0 $f(x, 2x^2) = x$
3) $0 \leq f(x,y) \leq x$ for all (x,y) with x>0
$g_1 (0,0) =g_2 (0,0) = 1$
I know f has no direction of maximal change because $f_1 (0,0)$and $f_2 (0,0)$are both 0, and so the gradient is zero and the angle between the gradient and any direction vector is undefined. How can this happen when the gradient is 1?