12. Let 3 \"W = {o (w) = (0,0) Let '5' = (a, b) be an arbitrary direction. 1. Compute the directional derivative (Dk)(0,0) of k at (0, 0) in the direction of '6. 2. Show that (Dk) (0, 0) is not a linear function of (a, b). In particular, show that we do not have D(a,b>k) (0, 0) = dk(o,g)(a, b) = km (0, 0):} + ky(0, 0)b. This shows that if we want to understand directional derivatives in terms of the partial derivatives (and we will!), we need to assume that the given function is differentiable