If we do not know any problem similar to ours that has been solved before, we may find our task pretty tough. If you connot solve the proposed problem, try to solve first some related problem. Could you solve a part of the problem? It may occur to us that if the square is privileged among quadrilaterals it must, by that very fact, also be privileged among rectangles. Apart of our problem would be solved if we could succeed in proving the following statement: "of all rectangles with given perimeter the square has the greatest area.