2.a.
XXXXX must XXXXXX XX XXXXXXX than 0, XX XXXX XXX following XXXXX
So, in XXXX cases XX have that XX , XXXX XX
, XXXX is .
Now if XX XXXX we XXX
, that is
.
2.b.
Therefore,
XX, .
so , so . XXXXXXXXX, .
Thus, it XX XX XXX next XXXX