Seriously, are you eventryingto do these problems yourself? Do you not see that "-7n+ 49= 7(-n+ 7)" is divisible by 7 for all n? What does that mean for "?

No, that is not a "disproof by counter example" because the problem does NOT assert that " is divisible by 7 foralln". The problem is to show that thereexistsat least one such n. The fact that there exist n for which it is NOT true is irrelevant.

You have posted a large number of widely diverse problems in which you seem to have no idea what they are about or even what they are asking. What is going on here?