6. Let $S \subset \mathbb{R}$ be a nonempty bounded subset. Given $k \in \mathbb{R}$ define $kS = \{ks : s \in S\}$. Prove the following: (a) If $k > 0$, then $\sup(kS) = k \cdot \sup S$. (b) If $k < 0$, then $\sup(kS) = k \cdot \inf S$.
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b) If k < 0, then sup(kS) = inf(S) bounded above. Show more…
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