, the rate of change of f with respect to x is zero on I and hence f is constant In view of the above remark, it is justified to infer that the family {F + C, C ∈ R}
provides all possible anti derivatives of f We introduce a new symbol, namely, 
( )
∫f x dx
 which will represent the entire
class of anti derivatives read as the indefinite integral of f with respect to x Symbolically, we write 
( )
f x dx= F ( ) + C
x
∫