Thread: just a few simple questions on set

Let S={1,2,3}. Then ∅⊆ S. Why is this true?

∅⊆{∅}. Why is this true?

The set {x∈ ℚ : 2x2 - 7x- 4 =0}. How come this one has 2 elements instead of 1?

Thanks.

Originally Posted by naturebuilder

Let S={1,2,3}. Then ∅⊆ S. Why is this true?
∅⊆{∅}. Why is this true?

The statement that means that
So for any set it is true that