Now,
we consider the easy and intuitive way of
finding the area bounded by the curve
y = f (x), x-axis and the ordinates x = a and
x = b From Fig 8 1, we can think of area
under the curve as composed of large
number of very thin vertical strips Consider
an arbitrary strip of height y and width dx,
then dA (area of the elementary strip)= ydx,
where, y = f(x)