Open subset
1. Let A ={ x ∈ R : 0 < x^2+x-12 < 8}.
Show that A is an open subset of R.
2. Suppose U is an open subset of R and let B = { x ∈ R : y=2x ∈ U }
Show that B is an open subset of R.
Compact
For each of the following sets, sketch the set, and determine whether it is
compact.Why?
1. A={x∈R：1<|x|<=3}
2. For fixed positive integer k, let B_k = {x ∈R：|x|<=1-(1/k)}
∞
3. C= ∪ B_k where B_k are the sets defined in part (b.).
k=1
題目可能很簡單 因為我看不太懂題目
麻煩高手了
謝謝!
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※ 編輯: rayar 來自: 111.251.110.39 (02/09 21:13)