All Questions
Tagged with summation algebra-precalculus
974
questions
3
votes
4
answers
160
views
Proving $\sum_{i=0}^n (-1)^i\binom{n}{i}\binom{m+i}{m}=(-1)^n\binom{m}{m-n}$
I am trying to prove the following binomial identity:
$$\sum_{i=0}^n (-1)^i\binom{n}{i}\binom{m+i}{m}=(-1)^n\binom{m}{m-n}$$
My idea was to use the identity
$$\binom{m}{m-n}=\binom{m}{n}=\sum_{i=0}^n(-...
- 87
1
vote
3
answers
74
views
Attempt at creating a formula relating debt, payments and interest
I tried writing down a formula relating a given debt and interest to the periodic payments and number of payments.
So let's say someone starts off with a debt of $D$. The periodic interest is $r$ (for ...
- 1,037
3
votes
0
answers
35
views
Prove that $\sum_{r=1}^n (-1)^{r-1}(1+\frac{1}{2}+\frac{1}{3}+...\frac{1}{r}) \binom{n}{r} =\frac{1}{n}$. [duplicate]
Prove that $\sum_{r=1}^n (-1)^{r-1}(1+\frac{1}{2}+\frac{1}{3}+...\frac{1}{r}) \binom{n}{r} =\frac{1}{n}$. Where $\binom{n}{r}$ represents 'n choose r'.
I tried to simplify this expression by first ...
- 334
1
vote
1
answer
41
views
Conditions for $ \sum_{x\in G} f(x) = \sum_{x\in f(G)} x $ to hold
i have a question
what are the condition on the function $f$ ?
so that this equality hold :
$ \sum_{x\in G} f(x) = \sum_{x\in f(G)} x $
is $f$ surjective is a necessary for this question ?
please ...
- 11
1
vote
2
answers
82
views
Upper rectangle area sum to approximate 1/x between $1\leq x\leq 3$
I am trying to figure out how to use rectangles to approximate the area under the curve $1/x$ on the interval $[1,3]$ using $n$ rectangle that covers the region under the curve as such.
Here is what I ...
- 1,071
-1
votes
1
answer
70
views
Formula to increase x by y z times [closed]
What is the formula to increase x by y z times?
For example the number 4 I want to increase by 4 50 times. I added it out (4+8+12+16+20+24 etc....to 204) and got the right answer 5304 but what is ...
2
votes
4
answers
272
views
How did Rudin change the order of the double sum $\sum_{n=0}^\infty c_n\sum_{m=0}^n\binom nma^{n-m}(x-a)^m$?
I see many people change the order of sum but I don't understand how they did that.
Is there is a way to change the order of the sum, $\sum\limits_{k=a}^n\sum\limits_{j=b}^m X_{j,k}$ and $\sum\...
4
votes
3
answers
120
views
Show $\sum_{i=0}^n{i\frac{{n \choose i}i!n(2n-1-i)!}{(2n)!}}=\frac{n}{n+1}$
How can this identity be proved?
$$\sum_{i=0}^n{i\frac{{n \choose i}i!n(2n-1-i)!}{(2n)!}}=\frac{n}{n+1}$$
I encountered this summation in a probability problem, which I was able to solve using ...
user1253495
0
votes
0
answers
98
views
If $\sum_{i=1}^n x_i \ge a$, then what can we know about $\sum_{i=1}^n \frac{1}{x_i}$?
Suppose that $$\sum_{i=1}^n x_i \ge a$$
where $a>0$ and $x_i\in (0, b]$ for all $i$. Are there any bounding inequalities we can determine for $$\sum_{i=1}^n \frac{1}{x_i}?$$
I understand that $\...
- 1,615
1
vote
3
answers
66
views
I want to use integration for performing summation in Algebra
I am a class 9th student. Sorry if my problem is silly.
I am trying to find the sum of squares from 1 to 10. For this I tried summation, and it was fine.
But now I came to know that Integration can be ...
1
vote
0
answers
137
views
Simple algebra in rearring terms
I have a very simple mathematical question, and it is just about algebra which seems very tedious. First, let me state my problem from the beginning:
Let $i$ be an index representing countries ($i = {...
- 105
0
votes
0
answers
20
views
Finding a sufficient condition for dividends to be nonnegative
The Harsanyi dividend is defined as follows:
$d_v (S) = \sum_{R \subseteq S} (-1)^{|S|-|R|} v(R)$
Supermodularity is defined as follows, for $S \subseteq T \subseteq N$:
$v(S \cup \{i\}) - v(S) \leq v(...
- 43
2
votes
1
answer
128
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Let $A_{k}=\{0,... ,n\}\setminus\{k\}.$ How to prove $\sum_{k=0}^{n}\left[(-1)^{k+1}\prod_{\substack{i,j\in A_{k}\\i<j}}(a_{i}-a_{j})\right]=0$?
Let $A_{k}=\{0,1,\ldots,n\}\setminus\{k\}$ for each $k=0,1,\ldots ,n$.
I think that the following equality is true for all $n\in\mathbb{N}, n\geq 2$ :
\begin{align}
\sum_{k=0}^{n}\left[(-1)^{k+1}\...
- 23
1
vote
0
answers
98
views
Restructuring Jacobi-Anger Expansion
In Jacobi-Anger expansion, $$e^{\iota z \sin(\theta)}$$ can be written as:
$$e^{\iota z \sin(\theta)} = \sum_{n=-\infty}^{\infty} J_n(z)e^{\iota n \theta}$$
where $J_n(z)$ is the Bessel function of ...
- 31
2
votes
1
answer
47
views
Double Sum to Product Derivation
The function after the double-sigma sign can be separated into the
product of two terms, the first of which does not depend on $s$ and
the second of which does not depend on $r$. Source
Is the ...
- 1,818