List five elements in each of the following sets:

I am lost in Discrete Mathematics. I do not know what is being asked for these two questions.

List five elements in each of the following sets:

2d.) {n Î N | n^{2} + n is a multiple of 3}

List the (distinct) elements in each of the following sets:

1b.) {x Î Z | xy = 15 for some y Î Z}

I would like verification if this is accurate:

9a.) List all the subsets of the set {a,b,c,d} that contain:

i.) four elements - {a,b,c,d}

ii.) three elements - {a,b,c}, {a,b,d}, {a,c,d}, {b,c,d}

iii.) two elements - {a,b}, {a,c}, {a,d}, {b,c}, {b,d}, {c,d}

iv.) one element - {a}, {b}, {c}, {d}

v.) no elements - {0}

Re: List five elements in each of the following sets:

2d) list 5 natural numbers of the form $\displaystyle n^2 + n = 3p $ for some integer $\displaystyle p $ so one would be $\displaystyle 3^2 + 3 = 12 = 3 * 4 $

1b) list all the x's such that x*y = 15, for some integer y. so one element of the set is 3, since 3*5 = 15., another is -3, since -3*-5 = 15

9a)correct.

Re: List five elements in each of the following sets:

Thank you for you assistance and explanations. I am still new to this whole Discrete Mathematics and struggling a bit. The explanations helped to put these questions into perspective.