# Search results

1. ### Finding all tangent lines through a point

Homework Statement Find all tangent lines of the graph f(x)=x+3/x that have a y intercept of 4. Homework Equations The Attempt at a Solution Assume a is the x coordinate of a point of tangency. Thus the point of tangency is (a, a+3/a). We know the tangent line must pass...
2. ### Position on the plane of a man

Bah. Never mind, I was looking at something wrong. So would the set of all n=infinity locations be the whole argand plane? It seems that varying values the angle theta and the step function could eventually allow the sum of values to "converge" to any point on the plane.
3. ### Position on the plane of a man

Thank you guys, that takes care of the angle problem. So would the general nth position be Zn=1*e^(i0)+f*e^(i*theta)+...+f^n*e^(n*i*theta)? Somehow I doubt this is correct - shouldn't the radius continually be decreasing? Oops - I meant to the *horizontal*. After the initial step theta...
4. ### Position on the plane of a man

Homework Statement An man starts on 0+0i of the complex plane. During the first walk step he moves a distance 1 to the right and lands on 1+0i. At each walk phase after this initial one the walk length decreases by a factor f<1 and he changes direction by an angle theta (measured from the...

Thank you to both of you, that is reassuring to hear. I'll be sure to apply to programs outside the top ten. To be honest there are a lot of schools I would want to go to outside of the prestigious ones but from the research I've done it seems that obtaining a teaching position in academia...
6. ### Testing Exam nerves!

How well prepared were you for the exam? Did you know the material inside and out? I'm *not* saying this is parallel to your situation but something I used to regard as exam nerves was, at the crux of it, a lack of proper preparation. I studied, sure, but I didn't sufficiently prepare enough...

To elaborate on said situation - I went to a top 50 US public university for a few years majoring in math and during this period of time I had no significant interest or motivation in school, much less any graduate school aspirations. I didn't do *horrible*, but my gpa was about a 3.1. I took...

final bump
9. ### Fourier series convergence - holder continuity and differentiability

Sorry about the bump, but this question is killing me. I don't feel like the book explained this convergence criteria well at all.
10. ### Fourier series convergence - holder continuity and differentiability

I may be wrong about the holder condition, but it looks to me like f(x) is holder continuous as long as the exponent in the condition is equal to or less than 1/2.
11. ### Fourier series convergence - holder continuity and differentiability

Homework Statement Given each of the functions f below, describe the set of points at which the Fourier series converges to f. b) f(x) = abs(sqrt(x)) for x on [-pi, pi] with f(x+2pi)=f(x) Homework Equations Theorem: If f(x) is absolutely integrable, then its fourier series converges to f...
12. ### Countability subset of the reals proof

If we do this by contradiction wouldn't the negation be to assume that X and Y do not have cardinality equal to (a,b)?
13. ### Countability subset of the reals proof

Homework Statement Let (a,b)=XUY, X,Y arbitrary sets where (a,b) is an arbitrary interval. Prove that either X or Y has the same cardinality as that of (a,b). Homework Equations The Attempt at a Solution Really lost.
14. ### Intervals and their subsets proof

Ah completely overlooked that, thanks. I'll post up the full problem because now I'm sort of stuck.
15. ### Intervals and their subsets proof

Homework Statement I reduced another problem to the following problem: If I is an interval and A is a subset of I, then A is either an interval, a set of discreet points, a union of the two. Homework Equations The Attempt at a Solution Is this trivial?
16. ### Topology intervals on the real line proof

I suppose by z as the right endpoint if z is greater than or equal to all y in I and likewise for x. So if we define x to be the smallest element in I and z to be the largest, by the betweenness property we have that I contains every point in between x and z, i.e. for any x<y<z, y is in I...
17. ### Topology intervals on the real line proof

Ah forgot about the other direction. Let some subset of R be I such that I contains each point between any two of its points. Thus if x,z are in I and x<y<z, then y is in I. Let x,z be the endpoints of I. Thus by the betweenness property any y such that x<y<z implies y is in I. So I is an...
18. ### Topology intervals on the real line proof

Homework Statement a) Let I be a subset of the real line. Prove I is an interval if and only if it contains each point between any two of its points. b) Let Ia be a collection of intervals on the real line such that the intersection of the collection is nonempty. Show the union of the...

Thanks!
20. ### Differential geoemtry tangent lines parallel proof

Is the way I did it incorrect?
21. ### Differential geoemtry tangent lines parallel proof

Homework Statement Prove that a(s) is a straight line if and only if its tangent lines are all parallel. Homework Equations Frenet serret theorem The Attempt at a Solution I'm confused on the direction "if the tangent lines are parallel then a(s) is a straight line". Assume all the...
22. ### Diameter of a set

so how would I start the proof that the diameter is equal to the diagonal of the rectangle formed by the k-cell? it seems so simple but im having trouble seeing where to begin
23. ### Diameter of a set

Generally in this problem set if not specified, you couldn't assume a particular metric. But in any case I think its safe to assume its euclidean. Otherwise the diameter would just be infinite.
24. ### Diameter of a set

Ah thanks. Thats precisely what I confused on. I thought diam(K) meant the sup of all possible distance functions so it would have to be infinite, which made no sense. so I can take it that the question means the euclidean metric?
25. ### Diameter of a set

I think my main concern is how the euclidean metric yields the largest distance when there are an infinite amount of other possible metrics. How would that account for it?
26. ### Diameter of a set

Yes, thats what I mean. Isn't it true that they are as far apart as possible only in terms of the euclidean distance metric? In finding the diameter, aren't I supposed to find the least upper bound for all possible distance metrics on all possible points in this 2 cell, not just the euclidean...
27. ### Diameter of a set

Ah sorry. A 2-cell is a subset of R^2 of the form [a,b] x [c,d], or {(x,y) in R^2: a <= x <= b and c <= y <= d}. By diameter, since no distance function is specified, how do we know we can't define one that will give a value larger than the straight line path between the two farthest points in...
28. ### Diameter of a set

Homework Statement Define diam(X) of a set X, X a nonempty subset of arbitrary metric space, as diamX=supremum{distancefunction(x,y):x,y in X}. Let K be the two cell formed by two points a=(2,3) and b=(4,6) in the xy plane. Find diameter of K and show this is the diameter. Homework...