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Math Help - Uniform convergence of sequence of functions

  1. #1
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    Uniform convergence of sequence of functions

    Let {an},{bn}, {cn} be three sequence converges to a, b, c respectively.
    (a) Let B > 0 be a real number. Let fn(x) = an + bnx + cnx2. Show that {fn} converges uniformly to f(x) = a + bx + cx2 on [-B,B].
    (b) Prove or disprove that {fn} converges uniformly to f(x) on R.
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  2. #2
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    Re: Uniform convergence of sequence of functions

    I have no idea on part (b) how to prove or disprove on such set unbounded set R ?
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  3. #3
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    Re: Uniform convergence of sequence of functions

    Let $a_n = c_n = 0$ for all $n$. Let $b_n = 1+\dfrac{1}{n}$. Hence, $f_n(x) = \left(1+\dfrac{1}{n}\right)x$ and $f(x) = x$. Hence, $|f_n(x) - f(x)| = \dfrac{|x|}{n}$. Given any $\varepsilon>0$, if $|x|>n\varepsilon$, then $|f_n(x)-f(x)|>\varepsilon$. This is a proof by counterexample (it is not uniformly convergent).
    Last edited by SlipEternal; March 12th 2014 at 09:36 PM.
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