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Damascus Road
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Here's two more question I'm working on in test prep.
2.) Let Y = [-1,1] have the standard topology. Which of the following sets are open in Y, and which are open in R.
A= (1,1/2) [tex]\cup[/tex] (-1/2,-1)
B= (1,1/2] [tex]\cup[/tex] [-1/2,-1)
C= [1,1/2) [tex]\cup[/tex] (-1/2,-1]
D= [1,1/2] [tex]\cup[/tex] [-1/2,-1]
E= [tex]\cup[/tex] [tex]\frac{1}{1+n}, \frac{1}{n}[/tex] (union is from n=1 to infinity)
So, to start, I should I examine their complements?
My gut feeling is that A,B are open in R and C, D are open in Y and I'm not sure about E. 3.) I need to prove:
Let X be a topological space, and let Y [tex]\subset[/tex] X have the subspace topology. Then C [tex]\subset[/tex] Y is closed in Y iff C = D[tex]\cap[/tex] Y for some closed set D in X.
This has be a bit confused...
A subspace topology on Y is defined as
[tex] T_{Y} = {U \bigcup Y | U is open in X} [\tex]
So, simply, if D were open... it's basically the exact definition that I provided. Which gives that U is open.
2.) Let Y = [-1,1] have the standard topology. Which of the following sets are open in Y, and which are open in R.
A= (1,1/2) [tex]\cup[/tex] (-1/2,-1)
B= (1,1/2] [tex]\cup[/tex] [-1/2,-1)
C= [1,1/2) [tex]\cup[/tex] (-1/2,-1]
D= [1,1/2] [tex]\cup[/tex] [-1/2,-1]
E= [tex]\cup[/tex] [tex]\frac{1}{1+n}, \frac{1}{n}[/tex] (union is from n=1 to infinity)
So, to start, I should I examine their complements?
My gut feeling is that A,B are open in R and C, D are open in Y and I'm not sure about E. 3.) I need to prove:
Let X be a topological space, and let Y [tex]\subset[/tex] X have the subspace topology. Then C [tex]\subset[/tex] Y is closed in Y iff C = D[tex]\cap[/tex] Y for some closed set D in X.
This has be a bit confused...
A subspace topology on Y is defined as
[tex] T_{Y} = {U \bigcup Y | U is open in X} [\tex]
So, simply, if D were open... it's basically the exact definition that I provided. Which gives that U is open.
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