Q: If y is in R, y>0, then there is a positive integer n such that 1/n<y.

A: All I can think of is to use the fact that N is unbounded, thus for any value of y I can creat a smaller fraction with a larger value of n.

Also,

Q: Consider the set A={1/n : n is in R}. Prove that inf(A)=0.

Any help understanding how to do these would be much appreciated. Thank you.