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Q A for people studying math at any level and professionals in related fields
- (Un-)Countable union of open sets - Mathematics Stack Exchange
A remark: regardless of whether it is true that an infinite union or intersection of open sets is open, when you have a property that holds for every finite collection of sets (in this case, the union or intersection of any finite collection of open sets is open) the validity of the property for an infinite collection doesn't follow from that In other words, induction helps you prove a
- Mnemonic for Integration by Parts formula? - Mathematics Stack Exchange
The Integration by Parts formula may be stated as: $$\\int uv' = uv - \\int u'v $$ I wonder if anyone has a clever mnemonic for the above formula What I often do is to derive it from the Product R
- The sequence of integers - Mathematics Stack Exchange
Prove that the sequence $\\{1, 11, 111, 1111, \\ldots\\}$ will contain two numbers whose difference is a multiple of $2017$ I have been computing some of the immediate multiples of $2017$ to see how
- $\\operatorname{Aut}(\\mathbb Z_n)$ is isomorphic to $U_n$.
It might be using ring theory in a non-essential way, but it is conceptually simpler because the endomorphisms are easier to describe than the automorphisms, and since the invertible elements of Zn Z n are by definition Un U n, we obtain the result without having to understand what Un U n actually looks like
- Prove that the sequence (1+1 n)^n is convergent [duplicate]
It is hard to avoid "the concept of calculus" since limits and convergent sequences are a part of that concept On the other hand, it would help to specify what tools you're happy with using, since this result is used in developing some of them (For example, if you define ex = limn→∞(1 + x n)n e x = lim n → ∞ (1 + x n) n, then clearly we should not be using ex e x in the process of
- probability - If $U\sim U (-1,1)$ and $N\sim N (0,1)$ are independent . . .
If X2 X 2 is not constant, then we cannot have independence between X X and XN X N In particular, if U U follows a uniform law on [−1, 1] [1, 1] (or any interval), the random variables U U and UN U N are not independent
- How to parametrize a triangle? - Mathematics Stack Exchange
How do I parametrize a triangle with vertices A(1, 1) A (1, 1), B(2, 2) B (2, 2) and C(1, 3) C (1, 3)? I have tried working with the equations of the lines that form it but am not completely sure how to link them together to come up with a parametrization of the form r(t) r (t)
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