Recent content by Frillth

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    Measure of Irrationals with Even First Digit

    Hahaha, of course. Man, it is clear that I haven't slept for a while. Thanks, Hurkyl. Edit: Well, since my first question was pretty stupid, I have a new one to ask. Is it possible to divide up the irrationals from [0,1] into two sets A and B such that each set contains "half" of the...
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    Measure of Irrationals with Even First Digit

    I just finished a course where we discussed concepts such as Lebesgue integration and Lebesgue measure of sets. Today, I was telling my brother about how the irrationals on the interval [0,1] have measure 1, which is sort of counter-intuitive. Anyway, he proposed the following question. Let A...
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    Find 3x3 Rotation Matrix for Rotated x`y`z` Space

    Homework Statement I need to find a 3x3 rotation matrix that takes a point in regular cartesian space and gives its coordinates in a rotate x`y`z` space. The +z` axis runs along the vector [1,1,-1], and the +x` axis should be in the xz plane with positive x component. Homework Equations The...
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    Why Does Sound Travel at a Constant Speed in a Medium?

    I know from my physics course that sound has a particular speed in any medium that it is traveling through, much like light. I have not learned, however, why this is so. I know that sound is simply a pressure wave traveling through air (or water or steel or whatever), but it doesn't seem...
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    Mutual Inductance: Solving with Ampere's Law

    Can I use Biot-Savart to find the magnetic field at some general point (x,y) in the plane, then integrate that over the area of the top loop to get flux?
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    Mutual Inductance: Solving with Ampere's Law

    Homework Statement Homework Equations Φ = M*I Biot-Savart law Ampere's law The Attempt at a Solution I have the formula Φ = M*I, which means that to find the mutual inductance I simply need to find the magnetic flux through the top circuit due to the current in the bottom...
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    Solving a Physics Problem Involving a Square & Magnetic Field

    Homework Statement I have the following problem for physics homework: We are supposed to take t=0 as the instant when the corner of the square is just about to leave the magnetic field. Homework Equations Unsure. The Attempt at a Solution Since the magnetic flux will decrease as the...
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    Volume of a Restricted Region in n-Dimensional Space

    I did it by induction on n. How would you approach it with your second method?
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    Volume of a Restricted Region in n-Dimensional Space

    The volume of that should be (I think): Is there a simple way to evaluate this, or am I doing this completely wrong? By the way, sorry if that's hard to read. I don't know latex, so I just used Mathematica. Edit: Ah, I just realized how to compute that integral. It comes out to n^n/n...
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    Volume of a Restricted Region in n-Dimensional Space

    Homework Statement Let S = {x∈R^n : x_i ≥ 0 for all i, x_1 + 2x_2 + 3x_3 + ... + nx_n ≤ n}. Find the n-dimensional volume of S. Homework Equations I'm 95% sure that I'm supposed to use the change of variables theorem here. The Attempt at a Solution So far, I have calculated the values for...
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    How Do You Calculate Equivalent Capacitance in Complex Circuits?

    Homework Statement I need to find the equivalent capacitance between points 1 and 2 in the following circuit, with each capacitor having capacitance C: Homework Equations For n capacitors in series: 1/C_t = 1/C_1 + 1/C_2 + ... + 1/C_n For n capacitors in parallel: C_t = C_1 + C_2 + ... +...
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    Inverse/Implicit Function Theorems

    Homework Statement Let B=B(0,r) be an open ball of radius r centered at the origin in R^n. Suppose U is an open subset of R^n containing the closed ball of radius r centered at the origin, f is a function from U to R^n that is differentiable, f(0) = 0, and ||Df(x) - I|| <= s < 1 for all x...
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    K-dimensional manifold problem

    Homework Statement Suppose X ⊂ R^n is a k-dimensional manifold and Y ⊂ R^p is an l-dimensional manifold. Prove that: X × Y = {[x,y] ∈ R^n × R^p : x ∈ X and y ∈ Y} is a (k+l)-dimensional manifold in R^(n+p). (Hint: Recall that X is locally a graph over a k-dimensional coordinate plane...
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    Volume in first octant cut off by a plane

    All right, so from there I take the partials and I get: dV/dy = (-12z^2 + 6z)/(12y + 12z - 6)^2 dV/dz = (-12y^2 + 6y)/(12y + 12z - 6)^2 Setting these equal to zero, I get: y = z = 0 and y = z = 1/2 However, I know that y and z can't be 0, and if y and z are 1/2, then by my earlier...
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    Volume in first octant cut off by a plane

    Homework Statement Find the equation of the plane through the point [1,2,2] that cuts off the smallest possible volume in the first octant. Homework Equations Volume of a pyramid = 1/3Ah The Attempt at a Solution The plane is going to cut out a pyramid with the x-, y-, and z-intercepts, so...
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