Is the Set M Closed in the Space X?

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SUMMARY

The discussion centers on whether the set M, defined as M={f ∈ C([0,1]) : ∫_{0}^{1}f(t)dt=2, f(1)=0}, is closed in the space X=(C([0,1]), || . ||_1). The user demonstrates that if a sequence f_n in M converges to f, then the integral condition ∫_{0}^{1}f(t)dt=2 holds. However, the user struggles with verifying the second condition, f(1)=0, and seeks clarification on the type of convergence being discussed, confirming that it is in the norm. The justification for the interchange of limit and integral is based on the continuity of the functions involved.

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Homework Statement


Let X=(C([0,1]), || . ||_1 ), where ||f||_1=\int_{0}^{1}|f(t)|dt.
Let M=\{f \in C([0,1]) : \int_{0}^{1}f(t)dt=2, f(1)=0\}.
Is M closed in X?

The Attempt at a Solution



I've tried the following:
Let f_n be a sequence in M such that f_n \rightarrow f.
I'm checking whether f \in M, because that would prove that M is closed (if a set contains all the limits of its convergent sequences, it is closed).
There are obviously two conditions to check.
The first one:
\int_{0}^{1}f(t)dt=\int_{0}^{1}limf_n(t)dt=lim\int_{0}^{1}f_n(t)dt=lim 2=2.
Now I have to check the second one, that is, is f(1)=0, and I don't know how.

Any help is much appreciated.
 
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If f_n(1)= 0 and f_n\rightarrow f, then... (What kind of convergence are you talking about? Pointwise? Uniform? In the norm?)

And is your justification for saying
\int_0^1 limf_n(t)dt= lim\int_0^1 f_n(t)dt?
 
HallsofIvy said:
If f_n(1)= 0 and f_n\rightarrow f, then... (What kind of convergence are you talking about? Pointwise? Uniform? In the norm?)

In the norm.

And is your justification for saying
\int_0^1 limf_n(t)dt= lim\int_0^1 f_n(t)dt?

My justification would be that f_n are continuous functions, so integral and limit commute.
 

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