Recent content by JThompson

  1. J

    Proving the Existence and Non-Existence of Limits: A Basic Proof Guide

    P\implies Q was supposed to relate to the "if |x-c|<delta, then |f(x)-L|<epsilon" part of the epsilon-delta definition. Essentially, this statement is equivalent to |x-c|\geq\delta\mbox{ or } |f(x)-L|<\epsilon. So negating this portion of the definition returns |x-c|<\delta\mbox{ and }...
  2. J

    Proving the Existence and Non-Existence of Limits: A Basic Proof Guide

    Here are a few hints: P\implies Q is equivalent to \neg P\vee Q. So the negation of the statement is P\wedge\neg Q. Negated universal quantifiers become existential, and negated existential quantifiers become universal.
  3. J

    Undergrad How to find a logical statement equivalent to the one I have?

    The closest thing I could find is a Wikipedia table of valid argument forms in propositional logic. http://en.wikipedia.org/wiki/Propositional_logic#Basic_and_derived_argument_forms"
  4. J

    Finding values of delta that correspond with M=Any Number

    The point is that this means nothing without context- we have absolutely no idea what you are talking about. However- wild guess- are you trying to find a delta such that 0<x<\delta implies \cot (x) > m ?
  5. J

    Undergrad Understanding Ordered Fields: A Beginner's Guide

    Firstly, a subset does not necessarily have all of the same properties as any of its supersets, so it's perfectly reasonable that a subset of R would not satisfy the Completeness Axiom. Consider \{x\in \mathbb{Q}: x\leq \sqrt{2}\}. Is there a least upperbound for this set in Q? No, because Q...
  6. J

    Calculus 2 question (∫cos^3(x)dx)

    This problem is much easier if you use the formula cos^2(x) = 1-sin^2(x). In general, try simple formulas before more complicated ones. (This is of course relative, but I classify a simple formula as one that comes up often and is extremely easy to remember.) Also ∫(cosx)/2dx is 1/2sinx, not...
  7. J

    Why can't we let z = 2 in this parametric surface?

    If you set z=2 you have the parametrization of a circle, not a cylinder. You do know that the cylinder is bounded, but you have to let z vary to obtain a cylinder. Here's the thing. When you do these sorts of problems, the position vector is only part of the parametrization. The position vector...
  8. J

    I am a lot of problems with parametrizing surfaces

    Based upon the intervals you wrote down, it looks like you are trying to find a single parametrization for the whole surface- don't try that. This will not work because the pieces of the surface, i.e. the cylinder and the two planes, have different normal vectors. 1) Do you see why they...
  9. J

    Surface integral parametrization

    Your parametrization does not need to include the cone because the problem concerns the surface S, which is just part of the sphere. As Dick was saying, the cone is only relevant to your limits of integration- you do not need to parametrize the cone because it is not part of S.
  10. J

    Does This Improper Integral Converge or Diverge?

    Just to be clear, the antiderivative of \frac{x}{\sqrt{1-x^2}} is not - \frac{1}{2\sqrt{1-x^2}}. It is -\sqrt{1-x^{2}}.
  11. J

    How Do I Solve Trigonometry Word Problems for My Exam?

    I'm not sure what you mean by this. If you let h be the height of the house, then the whole thing should be h+4.5 . This should be a side of the triangle with a 59.5 degree interior angle opposite this side. Then you'll have another triangle with an interior angle of 56.3 degrees with an...
  12. J

    Restrictions of denominators with negative exponents.

    I was taught to remove negative exponents when determining the domain of a function, but it is entirely possible my teacher was incorrect. If this were a composite function, say f(x)=x^{-1} and g(x)=\frac{1}{x^2}, then the domain of g(f(x))=\frac{1}{(x^{-1})^{2}} would definitely be x\neq 0...
  13. J

    Solving Difficult Limits: Expert Tips for x->0 EXP(-1/X*2)/X

    This is an indeterminant form, 0/0. Have you learned how to handle these?
  14. J

    Restrictions of denominators with negative exponents.

    Yes, \frac{1}{x^{-2}}=x^{2}. By restrictions, do you mean domain restrictions? No it does not have a hole at x=0, since x^{2} does not. In general it is a good idea to convert the denominator to non-negative exponents before analyzing where the equation is defined, but this is mostly because...
  15. J

    Differential equation (product/quotient)

    Yes. The derivative will be of the opposite sign. v'(x)*u(x)-u'(x)*v(x)= -(u'(x)*v(x)-v'(x)u(x)) Good luck.