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Homework Statement
[tex]fn(x)=n\chi_{(0,n^{-1})}(x)-n\chi_{(-n^{-1},0)}(x)[/tex] -1<x<1
Prove that [tex]\int fn(x)dx\rightarrow\int f(x)[/tex]
a. Using direct computation
b. Use dominated convergence
The Attempt at a Solution
a. How to do direct computation?
b. Using dominated convergence
If x is in (0,1/n), then fn(x)=<1-0=1
If x is in (-1/n,0), then fn(x)=<0-1=-1
If x is in neither , then fn(x)=0
Thus |fn(x)| is dominated by |g| where g(x)=1 , a constant function on (-1,1)
g(x) is in L1, since g(x) is Riemann integreable on (-1,1) it must also be Lebesgue integreable.
Thus, by dominated convergence theorem:
"limit of integration of fn" is equal to "integration of limit of fn"= integration of f(x)=0 as n goes to +infinity.
Thus,
[tex]\int fn(x)dx\rightarrow\int f(x)\rightarrow0 [/tex] QED