Say that X ⊆ Ris closed under multiplication if for all x, y ∈ X, we have that xy ∈X. a. Give three examples of finite subsets of Rwhich are closed under multiplication. b. Give an example of an infinite proper subset of Rwhich is closed under multiplication. Prove your answer. c. Give an example of an infinite proper subset of Rwhich is not closed under multiplication. Prove your answer.

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