Suppose that two intersecting lines are both level curves for a diff erentiable function f(x; y). (i) Show that the point where the two lines...

Suppose that two intersecting lines are both level curves for adifferentiable function f(x; y).(i) Show that the point where the two lines intersect must be a critical point.(ii) Must this critical point be a saddle point? (If YES, explain why; if NO, give acounterexample).