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For questions that explicitly reference the binomial coefficients, Pascal's Triangle, and Binomial identities.

5 votes
3 answers
936 views

How to find the coefficient of $x^k$ in the expression $\prod_{p=1}^n (x^p+1)^p$?

I tried to find the indefinite integral $$ f_n(x)=\int \prod_{k=1}^n \cos^k(kx) \, dx$$ by using Euler's formula and put $x=\frac{\ln y}{2i}$ I got $$ f_n(x)=-i2^{-\frac{n(n+1)}{2}-1}\int y^{-\frac{n( …
Faoler's user avatar
  • 513
4 votes
Accepted

How to find the coefficient of $x^k$ in the expression $\prod_{p=1}^n (x^p+1)^p$?

I got it ... firstly the degree of $(x^p+1)^p$ is $p^2$ So the degree of $\prod_{p=1}^n (x^p+1)^p$ is $$N=1+2^2+3^2+...+n^2=\frac{n(n+1)(2n+1)}{6}$$ now we have $$\prod_{p=1}^n (x^p+1)^p=\sum_{p=1}^N …
Faoler's user avatar
  • 513
4 votes
2 answers
216 views

how to prove identity for nth derivative of $(\text{arctanh}(x))^j$?

this question asked on MSE I worked on integral problem and I got that $$ \int_0^1 \frac{x^n}{\ln \left(\frac{1-x}{1+x} \right) } dx=-\frac{2}{(n+1)!}\sum_{j=1}^{n+1}F(n,j) \eta'(-j)$$ where $\eta(x)$ …
Faoler's user avatar
  • 513