# Search results

1. ### Inductive proof in complex arithmetic

Actually the formula is \cos x = \frac{e^{ix} + e^{-ix}}{2} but the general idea of using this formula was very helpful! It's a lot easier to show this directly by plugging in that formula and using the geometric sum formula, than to use induction. Cool problem though! Thanks guys.
2. ### Inductive proof in complex arithmetic

Oh yeah! I saw it before in first year but it's been a while since then, lol. That's not really too in-depth but the only stuff I've done with complex numbers was studying inner product spaces, and all we didn't need stuff complex exponential notation to do that. But yeah I'll try that formula...
3. ### Inductive proof in complex arithmetic

Which complex notation are you talking about? We actually haven't learned much about complex numbers in particular ... It's an analysis class, so the prof defined \mathbb{C} as \mathbb{R}^2 with "funny multiplication" and then we immediately started talking about Cauchy sequences, topology...
4. ### Inductive proof in complex arithmetic

Sorry sorry sorry I mistyped the question! Certainly summation begins with k = 0.
5. ### Inductive proof in complex arithmetic

Homework Statement Prove that for any n \in \mathbb{N} and x \in \mathbb{R}, we have \sum_{k = 0}^{n} {\cos{(kx)}} = \frac{1}{2}+ \frac{\cos{(nx)} - \cos{[(n+1)x]}}{2 - 2\cos {x}} Homework Equations None I can think of. The Attempt at a Solution Try induction. The result holds if n = 0...
6. ### Non-convergent power series but good approximation?

^ Power series are just polynomials, right? So essentially you're approximating using low-order polynomials. I don't know anything about QM but that'd be my guess as to why what you're doing is reasonable.

8. ### Integrals on arbitrary (bounded) domains

Homework Statement Let A = \{(x, y, z) \in \mathbb{R}^n : 0 \lt x \leq 1, 0 \lt y \leq 1 - x^2, 0 \lt z \leq x^2 + y\}. Define f : A \rightarrow \mathbb{R} by f(x, y, z) = y for each (x, y, z) \in A. Accept that Fubini's theorem is applicable here. Find \int_A f. Homework Equations Fubini's...
9. ### Apostol definition of interior point and open set

Hopefully this will clear some stuff up. Let S \subseteq \mathbb{R}^n. A point x \in S[\itex] is called an interior point of S if there exists a number r > 0 such that, whenever a \in \mathbb{R}^n is such that \Vert a - x \Vert < r, we have a \in S. To internalize this definition, let D_r(x) =...
10. ### Proving the proof by contradiction method

^ Yeah, I know about that stuff!! That's a super good idea, thanks a lot. I will upgrade my presentation to discuss transfinite induction. Thanks for the idea!
11. ### Proving the proof by contradiction method

I will show you what I have prepared on induction. My goal is to give new light on well-understood ideas, especially for freshman and juniors. Everyone learns mathematical induction in first year, so I just want to show a less common characterization of this concept. Let \mathbb{N} = \{1, 2, 3...
12. ### Proving the proof by contradiction method

I realize this. I'm presenting to undergrads, from freshman to seniors. Myself, I'm in my 2nd year. The only "axioms" I want to use are just simple intuitive things like that sets exist, that "set membership" is well-defined, that I can take unions, etc. Of course, considering my audience, I...
13. ### Does your school's math curriculum satisfy you?

The problem is that these new ideas are presented in the lecture. They're in the book too though. The theorem is drawn immediately after the definition is made, giving me no time to get intuition for a new concept and so I end up just scribbling down everything so I can read it later. It makes...
14. ### Does your school's math curriculum satisfy you?

Sometimes I feel like if I didn't ever have the gentle intro to calculus or linear algebra in high school, beginning in an abstract setting would be pretty tough. That might be part of the reason why calculus is (most often) presented before progression into real analysis. My first discussion on...
15. ### What is the simplest way of selecting the last N terms of a polynomial?

That only works for polynomials which can be expressed in the form (1 + x)n, though ...
16. ### Does your school's math curriculum satisfy you?

Does your school's math curriculum "satisfy" you? How much rigor is in your math courses? My school has a distinct math faculty (our math program is through the math faculty, not through sciences) with a variety of math majors: combinatorics, statistics, pure math, applied math, computation...
17. ### Basic sequence help. (Convergence)

^ Wut?? That's the result of convergence of a geometric series, it's very different. A sequence of real numbers (x_n) converges when there exists a number L \in \mathbb{R} such that, for any \epsilon > 0, I can find a number N \in \mathbb{N} so that |x_n - L| < \epsilon whenever n > N. This is...
18. ### Linear Algebra: Can't make sense of it!

Mepris, I recommend either of these books: Linear Algebra by Friedberg, Insel and Spence, or Linear Algebra by Hoffman and Kunze. Both good reads. The latter is slightly advanced but it seems like that's what you're interested in. As for partial fractions ... the coolest proof I've seen is a...
19. ### What is the simplest way of selecting the last N terms of a polynomial?

^ I think he might just mean an (ordered) set of terms from the polynomial. The order is established by listing the coefficients in descending order of their degree. I think what you want isn't so complicated. It's as follows: if p \in \mathbb{R}\left[x\right] is a polynomial with degree n...
20. ### Proving the proof by contradiction method

Proving the "proof by contradiction" method This can get a little bit fundamental or "axiomatic", if you will. Let's say we can describe sets by prescribing a fixed property P on objects of a certain type, and claiming that a set is a collection of objects satisfying P; i.e. A = \{x : P(x)\}...
21. ### Real Analysis - Study Group

Sounds good to me too, I can contribute online if possible. Feel free to inbox me. I have no background in analysis -- my first complex analysis course begins in January and I'll take Real Analysis I in May. Right now I'm taking my third calculus course in which we're discussing partial...
22. ### Newly found interest in maths

If you believe you have a good algebra (i.e. symbol manipulation) background, and understanding of basic and transcendental functions and basic geometry (polynomials, exponentials/logarithms, trigonometric functions; geometry of the circle, triangle and line), then I think Spivak is a great...
23. ### If space is not continuous, then is calculus wrong?

I've always thought that this was a result of a convenient choice of notation and measurement. Our units, although naturally chosen, are still human constructs. If we keep building on these constructs to develop things like calculus, then of course we will well-approximate physical phenomena --...
24. ### 1-norm is larger than the Euclidean norm

"1-norm" is larger than the Euclidean norm Define, for each \vec{x} = (x_1, \ldots, x_n) \in \mathbb{R}^n, the (usual) Euclidean norm \Vert{\vec{x}}\Vert = \sqrt{\sum_{j = 1}^n x_j^2} and the 1-norm \Vert{\vec{x}}\Vert_1 = {\sum_{j = 1}^n |x_j|}. How can we show that, for all \vec{x} \in...
25. ### Reusable formula for decrementing denominator

The relationship is nonlinear -- you can't find a common difference or ratio between each pair of adjacent terms. The relationship is as follows: if the term in question is 1 \over n, then the following term will be 1 \over n + 1. It's not really like you can add or multiply some constant to get...
26. ### Monotonically increasing/decreasing functions

To show that f is monotonically increasing, we need to show that for any \Delta{x} > 0, f(x + \Delta{x}) > f(x) for all x in the domain; or equivalently, f(x + \Delta{x}) - f(x) > 0. An equivalent definition is that f(x_1) < f(x_2) for all x_1, x_2 in the domain of f with x_1 < x_2. For your...
27. ### Schools Why isn't calculus taught in high school?

Advanced calculus, as in "calculus for the sake of calculus", is not really something science/engineering majors need to focus on. That's why applied calculus is offered at pretty much any college. But I disagree when you say that it is a required course in college -- it isn't, outside of...
28. ### Exponential function question

^ What's "LIM"? Do you mean n is any positive integer? I suppose the job to be done here is to find which value of k maximizes the expression in question. Let Q_n(k) be that expression. The problem is to find k_0 such that, for each n, Q_n(k_0) \geq Q_n(k) for all k -- and subsequently, to show...
29. ### For tiny h, f(x+h) = f(x) + hf'(x) ?

It's pretty inaccurate in a rigorous mathematical context, for sure. But I bet the book you were reading wasn't really oriented for pure math, rather for engineering or science, amirite?
30. ### For tiny h, f(x+h) = f(x) + hf'(x) ?

I see that you were referring to yourself there. But you make your point by saying that you are a mathematician, justifying that you should not write that. It's pretty clear that you're just saying "a mathematician should not write something like this". Of course I don't disagree with you in...