, xr = a + rh and
xn = b = a + nh or b
a
n
−h
=
 We note that as n → ∞, h → 0 Fig 7 2
O
Y
X
X'
Y'
Q
P
C
M
D
L
S
A
B
R
a = x0 x1 x2
xr-1 xr
x =b
n
y
f x
 = ( )
332
MATHEMATICS
The region PRSQP under consideration is the sum of n subregions, where each
subregion is defined on subintervals [xr – 1, xr], r = 1, 2, 3, …, n