This is a very first lecture in Optimization & Calculus of Variations. Here I'm going to discuss about basic concept of functional, and will prove a important result pertaining to the necessary condition for the existence of the extremal of the given functional. This will be instrumental for all those students who are studying mathematics in Sr. Secondary, under graduate and post graduate etc. across the globe. Do like , comment & share my video. Also don't forget to subscribe to my you tube channel.