Recent content by joeblow

  1. J

    Spacecraft path with polar coordinates

    There is a circular gate rotating at a constant angular speed of ω. The circular gate has a tunnel across its diameter. The mission is to pass through the gate. (That is, come in one side of the gate, travel the whole diameter, and exit at the other side.) Also, craft is neutrally buoyant...
  2. J

    Interpreting and Solving a Vector Calculus Question

    That annoys me. To me, that notation defines a ray and not a vector. Apparently, I'm not in the loop on that one.
  3. J

    Interpreting and Solving a Vector Calculus Question

    Does MA mean the vector connecting M and A? If so, what's wrong with using subtraction so that the problem is clear?
  4. J

    Interpreting and Solving a Vector Calculus Question

    If A, B, and M are all position vectors, then AM and BM have no readily apparent definition.
  5. J

    Interpreting and Solving a Vector Calculus Question

    Okay. I'm now confused. What is M? The only thing that would make sense would be if M is a scalar, but then the locus of M would not be a surface, since it lives in the straight line of the real numbers.
  6. J

    Symbol for partial derivative not used for partial integrals?

    The expression \partial x is precisely equal to dx if all other "variables" are kept constant. Thus, in iterated integrals, where you *do* keep all variables constant, dx = \partial x.
  7. J

    How to Evaluate the Integral \(\int_0^{∞} \frac{e^{-(x+x^{-1})}}{x}dx\)?

    My guess is that you express e = (1+1/x)^x then work with that.
  8. J

    Summation with exponential functions

    The terms are a composition of \left(\frac{1}{z}\right)^k and e^z . There should be a nice geometric series formula for this.
  9. J

    What is the Definition of Limit in Real-Valued Spaces?

    If your set is open, then every point is an interior point and can be enclosed inside a ε-disc. This ensures that it can be approached by all directions, as needed by the definition. If you are working with a closed set as your domain, your boundary points are still being approached in all...
  10. J

    A frustrating limit of a function f(x,y)

    \underset{(x,y)\rightarrow (0,0)}{\lim}=\frac{x^2\cdot \sin^2 y}{x^2+y^2}=\cos^2 \theta \sin ^2 (r\sin \theta)) where θ is the angle of (x,y). Does that help at all? Edit: I put a mult. sign where the + sign should be! o_O
  11. J

    Definitions and properties of limits (handwriting attached)

    Suppose we have the graph of a function. Let us approximate its shape with vectors whose horizontal component is dx and vertical component is dy. Then, the derivative of the function gives us the number we need so that dx \cdot \frac{dy}{dx}=dy. (Typically, y is dependent on x, so we can...
  12. J

    Definitions and properties of limits (handwriting attached)

    Well... I'd say that it "makes sense" only if it were a definite integral. And I wasn't complaining about the uselessness of the proof, so much as the impossibility of computing the integral on the RHS. I hope you're not using this to "prove" FTC. If you are, you should consider the change of...
  13. J

    Definitions and properties of limits (handwriting attached)

    If dy and dx have been properly defined (which for some reason is a rare occurrence), then this equality is immediately apparent for differentiable functions. However, this is useless as a means to finding an antiderivative (which is what you're doing, since you have no bounds on your...
  14. J

    Understanding the Lagrangian Function for Maximization Problems

    Definitely not enough info here for anyone to understand what's going on. For instance, "solve for FOC for the lagrangian function with respect to r(y,a)" is meaningless to me.
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