According to quadratic mathematical function, movement of an interection point of two f(x) varies area of figure made by two curves of graphs and x-axis.Thus, I apply the movement of the interection point of two curves on legs of stool to change area of seat, which becomes wider and narrower.
F(x) is mathmatical fuction. However, the word of function is not only using in math but also using as ability.
Therefore, I apply the concept of f(x) and it brought the additional function, which is feature that easy to movable frequently than chair or sofa. Because, we use it for simple sitting rather than for comfort. So, stool has big seat board, has little attraction. But too small seat board makes big user uncomfortable. So we sometimes wish seat area of stool is bigger or smaller. As a result of using notion of quadratic function, stool gets additional function that is useful.