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Jul
23
comment How do I solve a under-determined quadratic multi-variate system?
I don't understand the question. Do you have the data points $(y,x_1,x_2,x_3)$ and are asking which $\beta_{\cdot}$ were used to make them work?
Jul
21
comment How to solve $z^3 + \overline z = 0$
@robjohn indeed, but not much harder and i wanted the OP to do at least something by himself
Jul
21
comment Proving whether linearly independent
@Mattos he meant $\ne$, like in programming
Jul
21
comment Given that $p$ is an odd prime, is the GCD of any two numbers of the form $2^p + 1$ always equal to $3$?
I don't quite get it -- if $p=2$, you get $2^p-1=5$ and if $p=3$ then $2^p+1=9$, but $gcd(5,9) \not =3$
Jul
21
comment Pagerank existence of a graph given a vector
@NikhilShinday new question did not come through. consider posting it as a separate question and pasting the link here
Jul
20
comment Determine all real $x$ for which the series $\sum\limits_{k=1}^\infty\frac{k^k}{k!}x^k$ converges.
if you substitute $x=1/e$ you get something very similar to the limit expression in the hint, can you use it?
Jul
20
comment Rewriting Triple Integral in different order
@sonia why don't you try yours and post the answer here, and i will check it?
Jul
20
comment Rewriting Triple Integral in different order
@sonia here is an example of a very related problem, just not yours.
Jul
20
comment Rewriting Triple Integral in different order
see the hint in the answer
Jul
20
comment Rewriting Triple Integral in different order
think about the region this represents and represent it using the different variable order; the integrand does not change
Jul
17
comment Find a non injective function between a set of integers and itself
pigeonhole principle implies this is impossible
Jul
17
comment Prove/disprove: if $X$ is an eigenvector of $T$ then X is a singular matrix
@Mnifldz i don't think so, $T$ maps matrix to matrix
Jul
16
comment Question on how to manipulate terms in this expression
Well, doesn't each of those sums depend on $x$? So the only constant seems to be $1/2^n$
Jul
16
comment Question on how to manipulate terms in this expression
i don't understand the question. constants wrt what quantity? $x$?
Jul
16
comment Upper bounding a definite integral
@IvoTerek it does, it's zero over $[0,1]$
Jul
16
comment Upper bounding a definite integral
if you just bound $f \leq 2$ then you get $$\int_0^5 2x = 25$$ which is better than your bound slightly, but still not good enough for $24$
Jul
16
comment Upper bounding a definite integral
@angryavian you're right
Jul
16
comment Upper bounding a definite integral
Must be, you didn't use the bound on $f$ at all
Jul
16
comment Upper bounding a definite integral
@angryavian it is actually $20\sqrt{5}/3 \approx 14.9 < 24$, so must have a bug
Jul
14
comment Conditional probability density function of X given Y = y
Please use LaTeX to typeset :)