Understanding LEADING and TRAILING operations of an operator precedence grammar
@Raphael : Definition of trailing : Any terminal which is present at the last of a right sentential form (and not the sentence) which is derived from a non-terminal is the trailing of that non-terminal.

Trailing($E$) : 

$E \rightarrow E + T$  --In this the trailing is '$+$'

$ \rightarrow E + T * F$ [using $T \rightarrow T*F$] -- Here trailing is '$*$'

$\rightarrow E + T * ( E )$ [using $F \rightarrow ( E )$] -- Here trailing is '$)$'

(from $E + T * F$) $\rightarrow E + T * id$ [using $F \rightarrow id$] -- Here trailing is '$id$'

Hence trailing($E$) = $\{+,*,),id\}$

So the lesson here is that you must use the right sentential forms also and not just the sentence to find out the trailing.

Note : $E \rightarrow E + T \rightarrow E + T * F \rightarrow E + F * id \rightarrow T + id * id \rightarrow F + id * id$ are all right sentential forms of $E$ as they have at least one non-terminal.

However $id + id * id$ is a sentence because it has no non-terminals and you must not use just the sentence to find out the trailing.