#2: The positive terms are:
1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7 + 1/8 + ... + 1/93 + 1/94 + 1/95
The negative terms are:
- 1/6 - 1/7 - 1/8 - ... -1/93 - 1/94 - 1/95 - 1/96 - 1/97 - 1/98 - 1/99 - 1/100
Cancelling the equivalent positive and negative terms, we are left with:
1 + 1/2 + 1/3 + 1/4 + 1/5 - 1/96 - 1/97 - 1/98 - 1/99 - 1/100
Now, it's calculator time!
#3: If you write out the factors, you have, for one of the factors, (-12 + 12) which is 0.
Therefore, the product is 0.