Reputation
116,791
Next tag badge:
393/400 score
156/80 answers
Badges
5 100 223
Newest
 Good Answer
Impact
~2.1m people reached

11h
comment Antiderivative of $\frac{e^x}{\sqrt{1-x^2}}$
A definite integral cannot result in an indefinite integral. For the third time: what is the other exercise? How does the solution to the other exercise use this one?
11h
comment What is the inverse function of gcd?
The hint is, think about how to express the gcd of two numbers in terms of the factorizations of the two numbers. If $r=2^73^45^8$ and $s=2^93^27^5$, can you tell me what $\gcd(r,s)$ is?
12h
comment What is the inverse function of gcd?
Do you know the Unique Factorization Theorem, lapin? Do you know how to express the gcd of two numbers in terms of their factorizations into primes?
12h
comment A question on the inequality $\bigl(\pi(x+y)\bigr)^2<4\pi(x)\pi(y)$
By the Prime Number Theorem, for every constant $C>1$, if $x$ and $y$ are large enough, then $\pi(x+y)<C(x+y)/\log(x+y)$ and $\pi(x)>(1/C)x/\log x$. That should give you a good start.
13h
comment Greek cross fractal
This is a math site. If you need some code, why not post to a coding site?
13h
comment Why in order to have the greatest term in the expansion of$ (1 + x)^n$, $x$ can't be greater than unity?
Why don't you take, say, $x=2$, $n=1/2$, and see what happens?
13h
comment program for checking isomorphic graph
Maybe this question belongs on a coding site.
13h
comment Find the number of flags of different types using induction
That's not the way to do things here, Samim.
20h
comment Antiderivative of $\frac{e^x}{\sqrt{1-x^2}}$
I don't follow. All I see at that link is some definite integrals. Your question is about an indefinite integral. Please: What is the other exercise? How does the solution to the other exercise use this one?
1d
comment An equality for the dimension of the sum of subspaces (in the non-degenerate case)
Thanks. So, what does it mean for a bunch of things to be "2 by 2 non-equal"? Is it different from just saying the things are distinct?
1d
comment An equality for the dimension of the sum of subspaces (in the non-degenerate case)
What does "2-2 distinct" mean?
1d
comment Student working with a researcher
Are you in the US? If you type research experience undergraduate math into Google, you'll find there are lots of programs there that do what you want to do, although most of them seem to be summer programs.
1d
comment Antiderivative of $\frac{e^x}{\sqrt{1-x^2}}$
Details, please. What's the other exercise? How does the solution to the other exercise use this one?
1d
comment Student working with a researcher
You are a student; you are taking math classes; go talk to the people teaching those classes. They know you (or at least they have access to your records) and are in the best position to help you.
1d
comment Counting the sum $\sum^{\infty}_{k=0} q^{k^{2}}$
What would count as an explanation for something not having an expression in finite terms? There are proofs, but they use pretty advanced stuff. Start by seeing what the web says about theta functions.
1d
comment Counting the sum $\sum^{\infty}_{k=0} q^{k^{2}}$
It's a theta-function. It can't be expressed in finite terms, in terms of the functions familiar from high school and 1st year undergrad math.
1d
comment this is a question of class 7 from integers
You tell us. How would you go about solving this problem? When you get stuck, someone will give you a hint.
1d
comment Question about Mersenne numbers
This is my understanding, as well. See, e.g., the Wikipedia piece on Mersenne primes, where it says, "It is also not known whether infinitely many Mersenne numbers with prime exponents are composite, although this would follow from widely believed conjectures about prime numbers...."
1d
comment Probability that two numbers differ by one bit
@barak, I think you are assuming that the two picked numbers are different, while robjohn is not making that assumption. The question says, "we pick two random numbers". Only OP knows whether the two numbers are guaranteed to be different.
1d
comment Given $N$, is there a formula for $card( \{(m,n)\, s.t.\, m\cdot n \leq N \} )$?
Well, it's not exactly an unsolved problem. The asymptotics are known, and bounds on the error term are known. The unsolved part is finding the best possible bound on the error term.