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**URGENT HELP PLEASEEEE, a question on set theory**

## Homework Statement

the question is:

Prove that these sets have cardinality aleph-nought:(there is two 2 prove)

(a) {1/(2^k) : k∈ℕ}

(b) {x∈ℤ : x >= -5}

im not sure how to work this out, please help on this, i did ask on a previous thread how to prove cardinality of a statement, thanks for your help guys