(3)
We observe that in (1), the function cos x is the derived function of sin x We say
that sin x is an anti derivative (or an integral) of cos x Similarly, in (2) and (3), 
3
3
x  and
ex are the anti derivatives (or integrals) of x2 and ex, respectively Again, we note that
for any real number C, treated as constant function, its derivative is zero and hence, we
can write (1), (2) and (3) as follows :
(sin
+ C)
=cos
d
x
x
dx
, 
3
2
(
+ C)
3
=
d
x
x
dx
and 
(
x+ C) =
x
d
e
e
dx
Thus, anti derivatives (or integrals) of the above cited functions are not unique