For setting up a formula for the integral, it is convenient to take elementary area in
the form of vertical strips As indicated in the Fig 8 13, elementary strip has height
APPLICATION OF INTEGRALS         367
y
=f x
(��)
X
Y
y
g x
=����(��)
x
=a
x
c
=
y
g x
=����(��)
y
=f x
(��)
x
b
=
A
B
R
C
D
Q
O
P
X′
Y′
f(x) – g(x) and width dx so that the elementary area
Fig 8 13
Fig 8