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Questions tagged [faq]

This is meant for questions which are generalized forms of questions which get asked frequently. See tag details for more information.

When you add a question marked faq, please also update the list of questions: List of Generalizations of Common Questions

The question which prompted this: Coping with *abstract* duplicate questions.

Note: Even though one might argue that tagging a question as faq should be enough, and there is no need to update the above list, updating the above list will serve to bring this policy back to attention and help raise awareness periodically.

112 questions
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Why is the even root of a number always positive?

Let $n \in \mathbb N$ be a natural number and $a \in \mathbb R$ be a real number. The $n$-th root of the number $a$ is defined as follows: Case I: $n$ is an odd number. In this case the $n^{\text{th}}$ root of $a$ is defined to be that number $b \in…
neesh
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What is the standard interpretation of order of operations for the basic arithmetic operations?

What is the standard interpretation of the order of operations for an expression involving some combination of grouping symbols, exponentiation, radicals, multiplication, division, addition, and subtraction?
Isaac
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Find the volume common to two circular cylinders, each with radius r, if the axes of the cylinders intersect at right angles. (using disk/washer)

Find the volume common to two circular cylinders, each with radius r, if the axes of the cylinders intersect at right angles. (using disk/washer) I saw no example of this problem anywhere.. I saw an example how to solve it without calculus but I'm…
J L
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When are the limit operations commutative?

I'll come up with a question that has bothered me for a long period of time. The question seems relatively simple, but I personally didn't manage to find an answer to it. In many cases I met problems where I had to deal with multiple limits and I've…
user 1591719
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Volume of the intersection of two cylinders

I have two infinite cylinders of unit radius in $\mathbb{R}^3$, whose axes are skew lines. Say that the axis of one is centered on the $x$-axis, and the axis of the other is determined by the two points $a$ and $b$. Is there a formula for the volume…
Joseph O'Rourke
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Single Variable Calculus Reference Recommendations

This question is a generalization of the common question asking for calculus references. It is here to abstract away the repetition, and give a canonical resource for calculus references. I'm looking for a resources to learn single-variable…
davidlowryduda
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How many equivalence relations on a set with 4 elements.

Let S be a set containing 4 elements (I choose {$a,b,c,d$}). How many possible equivalence relations are there? So I started by making a list of the possible relations: {$(a,a)(a,b)(a,c)(a,d)(b,a)(b,b). . .(d,d)$} {$(a,a)(a,b)(a,c). . . . . . . . .…
ncm
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Showing that $a^n - 1 \mid a^m - 1 \iff n \mid m$

Let $a\ge 2$ be an integer. Show that for positive integers $m,n$, we have $a^n - 1$ divides $a^m - 1$ if and only if $n$ divides $m$. I am having trouble showing this. I've seen a similar problem on here but it only shows one direction for the…
David
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Eigenvalues of the principal submatrix of a Hermitian matrix

This question aims at creating an "abstract duplicate" of various questions that can be reduced to the following: Let $A$ be an $n\times n$ Hermitian matrix and $B$ be an $r\times r$ principal submatrix of $A$. How are the eigenvalues of $A$ and…
user1551
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Proof of an estimate for the tail of a normal distribution

My advisor told me to look up the proof of the following standard estimate so that we can adapt it to the case where we are dealing with something similar but including the addition of a polynomial integrand. I have yet to find a reference…
user7980
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Find the Mean for Non-Negative Integer-Valued Random Variable

Let $X$ be a non-negative integer-valued random variable with finite mean. Show that $$E(X)=\sum^\infty_{n=0}P(X>n)$$ This is the hint from my lecturer. "Start with the definition $E(X)=\sum^\infty_{x=1}xP(X=x)$. Rewrite the series as double…
karfai
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Finding the limit of $\frac{Q(n)}{P(n)}$ where $Q,P$ are polynomials

Suppose that $$Q(x)=a_{n}x^{n}+a_{n-1}x^{n-1}+\cdots+a_{1}x+a_{0} $$and $$P(x)=b_{m}x^{m}+b_{m-1}x^{m-1}+\cdots+b_{1}x+b_{0}.$$ How do I find $$\lim_{x\rightarrow\infty}\frac{Q(x)}{P(x)}$$ and what does the sequence $$\frac{Q(k)}{P(k)}$$ converge…
Eric Naslund
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Find volume of crossed cylinders without calculus.

I found this puzzle here. (It's labeled "crossed cylinders".) Here's the description: Two cylinders of equal radius are intersected at right angles as shown at left. Find the volume of the intersection between the two cylinders, without using…
littleO
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Different ways of Arranging balls in boxes

This question is generalization of different cases of combinatorics problems that are generally asked. We will find general way of arranging $n$ balls in $r$ boxes. Cases : Identical Balls. Distinct Balls. Order considered. Distinct Balls. Order…
evil999man
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Confused between Nested Quantifiers

I am reading nested quantifiers. I am confused in between two cases, 1. Existential Quantifier before Universal Quantifier 2. Universal Quantifier before Existential Quantifier I would be very thankful if someone highlights the difference between…
user2857
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