12. For function f(x) = (ax)2, a, x E R", write Vf(x) and V2f(x). Is V'f(x) positive semi-definite

12. For function a, x e Rn, write and V 2 f Is positive semi-definite? 12. For function a, x e Rn, write and V 2 f Is positive semi-definite?