ABSTRACT
In Fig. 1, A is the area enclosed below the graph of f(x), above the x-axis and between the two vertical lines x = a and x = b. To find the area A we need first of all to find the total area beneath the same curve from the left up to some arbitrary point P on the curve where P has the coordinates (x, y). We shall denote this area by the symbol Ax (Fig. 2).
