about lagrangian dual in optimization. thanks in advance.

Let Co , CI , C 2 C K ER " and ri , 12 TheR . Consider the optimization problem OK min 10 - call 2 ( PH ) S . t . 1/20 - c/1 2 5 ? Vi = 1 K where . I is the 2 norm Argue that ( PK ) is a convex program and derive the lagrangian dual of ( PK )