Recent content by johnson12

  1. J

    Finding a C1 Function for Continuous f,g in Real Numbers

    Hello,I need some advice on a problem. Let f,g:R\rightarrow R (where R denotes the real numbers) be two continuous functions, assume that f(x) < g(x) \forall x \neq 0 , and f(0) = g(0).Define A = \left\{(x,y)\neq (0,0): y< f(x),x \in R\right\} B = \left\{(x,y)\neq (0,0): y> g(x),x \in...
  2. J

    Measuring Disjoint Sets with Lebesgue Outer Measure

    for (i) let d = d(X,Y), and O = \bigcup_{x\in X}(x - d,x+d) so O\bigcap Y = empty set, and X \subseteq O then since O is measurable we get: m(X\cup Y) = m((X\cup Y)\cap O) + m((X\cup Y)\cap O^{c}) = m(X) + m(Y).
  3. J

    Is the Set Defined by a Continuous Almost Everywhere Function Rectifiable?

    forgot to mention the definition of rectifiable here: a (bounded) set S is rectifiable if \int_{S} 1 exists. (so it has volume.)update: PROBLEM HAS BEEN SOLVED.
  4. J

    Proving m(X)=0: Sequence of Measurable Sets

    sorry that's only true if the E_{i} where increasing, but lim_{i\rightarrow\infty}\left(\sum^{\infty}_{j=i}m(X_{j})\right) =lim_{i\rightarrow\infty}m(X_{i}) . recall that if an infinite series converges you can make the remainder sum arbitrarily small.
  5. J

    Proving m(X)=0: Sequence of Measurable Sets

    you can say that m(X) <= m(E_{i}) for each i, and m(E_{i}) = lim m(X_{j}) = 0 since the sum was finite.
  6. J

    Is the Set Defined by a Continuous Almost Everywhere Function Rectifiable?

    let g:[a,b] -> R be a function that is continuous almost everywhere. assume that g(x) > 0 on [a,b]. Show that the set S = { (x,y): 0 <= y <= g(x) , a <= x <= b} is rectifiable. One way to attack it, is to show that S is bounded and boundary of S has measure zero. the problem I am having is...
  7. J

    Solving the Problem of an Infinite Chain Slipping Down a Table

    I get that T(\dot{x}) = \frac{1}{2}m \dot{x}^{2} U(x) = mgx , \frac{\partial L}{\partial x}= - m g \frac{d}{dt} \frac{\partial L}{\partial \dot{x}}= m\ddot{x} Lagranges equation implies m\ddot{x} + mg = 0 but I'm a little confused, if the chain is of infinite length, would it then...
  8. J

    Solving the Problem of an Infinite Chain Slipping Down a Table

    are you referring to this equation: \frac{\partial L}{\partial x_{i}} - \frac{d}{dt}\frac{\partial L}{\partial \dot{x_{i}}} = 0, i=1,2,3 where L = T - U is the lagrange function, how can I use this to model my problem? (ps. I am apologize if my physics is wrong, unfortunately I am a math...
  9. J

    Solving the Problem of an Infinite Chain Slipping Down a Table

    Hello all, I'm having trouble with the following problem: Pb: A chain with constant density and infinite length is slipping down from the table without friction. Determine the position of the tip of the chain at time t. I know there are a few ways to approaching this problem, namely from...
  10. J

    Uniform Boundedness of Derivative Sequence of C^1([a,b],R) Functions

    Youre right, the reason I ask is b/c I am trying to prove that every bounded sequence in C^1 has a convergent subsequence, Arzela Ascoli type problem.
  11. J

    Uniform Boundedness of Derivative Sequence of C^1([a,b],R) Functions

    Im having trouble showing that given a sequence of uniformly bounded C^1([a,b],R) functions, the derivative sequence is uniformly bounded. Any suggestions are helpfull
  12. J

    Gradient of f: R^2 -> R Defined by Integral Equation

    Define f: R^{2} \rightarrow R , by f(x,y) = \int^{sin(x sin(y sin z))}_{a} g(s) ds where g:R -> R is continuous. Find the gradient of f. I tried using the FTC, and differentiating under the integral, but did not get anywhere, thanks for any suggestions.
  13. J

    Proving Inequality for Continuously Differentiable Functions on Closed Interval

    Sorry for the discrepancy, the problem is to show that the supremum of |f(x)| over [0,1] is less than or equal to the integral from 0 to 1 of |f ' (x)|, where f ' (x) is the derivative of f.
  14. J

    Proving Inequality for Continuously Differentiable Functions on Closed Interval

    I'm having trouble with this inequality: let f be (real valued) continuously differentiable on [0,1] with f(0)=0, prove that sup_{x\in[0,1]} \left|f(x)\right| \leq \int^{1}_{0}\left|f\acute{}(x)\right| dx Thanks for any help.
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