e when Dt approaches zero) Hence, mathematically for an infinitesimally
small dt instantaneous rate is given by
[
]
[ ]
−∆
∆
=
=
∆
∆
av
R
P
r
t
t
(3 3)
As  Dt ® 0
or


 
inst
d
d
R
P
d
d
r
t
t


Table 3