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2d
comment How do you the roots of functions that are not quadratics?
(Answer to a deleted comment): It is when $-32\lt c\lt 0$.
2d
comment How do you the roots of functions that are not quadratics?
Note that the question does not ask you to find explicit formulas for the roots in terms of $c$. That can be done, but it is hard. It just asks how many (real) roots. The answer will depend on $c$.
2d
comment How do you the roots of functions that are not quadratics?
Good so far. Now imagine drawing various horizontal line $y=c$ and the picture will tell you the story.
2d
comment Why is every point in an open interval $(a,b)$ not a limit point?
Indeed they are all limit points of $A$. So are $a$ and $b$. The article does not say they are not limit points.
2d
comment What is the proof behind the mean confidence interval for a Binomial Distribution?
Little detail is supplied, but seems the normal approximation to the binomial is involved. To use it, we need to have the minimum of $np$ and $n(1-p)$ not too small.
2d
comment Easy question Find $\sin 2x$, $\cos 2x$, and $\tan 2x$
Use your correct calculations of $\sin(2x)$ and $\cos(2x)$, and divide. Note that the minus signs "cancel."
Jul
31
comment algebra question..
Nice question, thanks!
Jul
31
comment Inter-event time between 1st and 2nd events for Poisson Process
The first method in my answer to your previous question will do it.
Jul
31
comment How many two letter words can be formed from 26 English letters?
Imagine making a complete list, ordered alphabetically. On the first line, list all the words that begin with a. We get aa, ab,ac, and so on up to az. So there are $26$ words on the first line. On the second line, list all the words that begin with b, so ba, bb, bc, and so on. The second line has $26$ words. On the third line, list the $26$ words that begin with c. And so on. We have $26$ lines, each of which has $26$ words, for a total of $(26)(26)$.
Jul
31
comment Derivation of mean and variance of Hypergeometric Distribution
It is $E(X^2)-(E(X))^2$. The mean has been done a few times on MSE, and I remember doing most of the details of $E(X^2)$. But finding is not easy. However, a web search under mean and variance of the hypergeometric distribution yields lots of relevant hits.
Jul
31
comment Olympic sprinter
Hint: If we assume constant speeds (unreasonable) then when Carol travels $5$ metres, her slow sister only travels $4$. So when Carol has travelled $120$ metres, slow sister has travelled how many?
Jul
31
comment The existential theory is undecidable
In an existential formula negation (and implication) are allowed inside. For stuff connected with Hilbert's 10th problem, the distinction is usually not important, since one can replace $\lnot(P=Q)$, where $P$ and $Q$ are terms, by a negation-free existential formula, as in the four squares trick.
Jul
31
awarded  Nice Answer
Jul
31
comment The existential theory is undecidable
For existential positive, existential quantifiers (or none) in front, no logical connectives other than $\land$ and/or $\lor$ inside.
Jul
31
revised Distribution of time of Poisson process
added 39 characters in body
Jul
31
comment Determining polynomial values
There is insufficient information at this time.
Jul
31
answered Distribution of time of Poisson process
Jul
30
comment The existential theory is undecidable
Division is not an allowed operation in the language of rings. To describe the congruence condition, we want to say that $(x-1)/(t-1)-n$ is divisible by $t-1$, which means there is a $y$ such that $(x-1)/(t-1)-n=y(t-1)$, which means (multiply through by $t-1$) that there is a $y$ such that $x-1-n(t-1)=y(t-1)^2$, or equivalently $x-1=n(t-1)+y(t-1)^2$.
Jul
30
comment washer method calculus help
@BrianTung: My guess is that the source is in the English language.
Jul
30
comment washer method calculus help
"About $y=5$ is good enough. If in your original question you had written "the region bounded by $\dots$" you probably would have received an answer in under 5 minutes.