Consider the function f(x, y) =x²+y². sketch the level curves off (x, y) on the xy-plane for f(x, y) = c with c= 1,4,9,16. at the point (2,√5), compute the gradient vector. also draw pictures of ∇f, and duf when duf has a maximum and minimum. what happens if you take du(f) along a level curve? what θ values do these correspond to?