2. Let f (x. y, a) : I? | y2 l :2 (my bx; cyz, Where |a|

2. Let f (x, y, z) axy bxz cyz, where (a) Show that (0, 0, 0) is the only critical point of f. (b) Show that (0, 0, 0) is a local minimum of f. al < 2 and a2 b2 _4_ c2 _4_ abc < 4