Monday, 2 February 2015

summation - Sum with irrational powers and binomial coefficients



What is the value of:
nk=1((1)nk(n+1k+1)(51+5(3+5)k515(35)k52))?


I am stuck because of the binomial coefficient there, because without it the sum would just be a bunch of geometric series.


Answer



nk=1((1)nk(n+1k+1)(51+5(3+5)k515(35)k52))?



Here's a start.

I'm feeling too tired right now
to do more.



nk=1(n+1k+1)xk=n+1k=2(n+1k)xk1=1xn+1k=2(n+1k)xk=1x(1(n+1)x+n+1k=0(n+1k)xk)=1x((1+x)n+11(n+1)x)



Note that
(35)(3+5)=4.



If x=(3+5),



nk=1(n+1k+1)(1)k(3+5)k=1(3+5)((1(3+5))n+11+(n+1)(3+5))=(35)4((1)n+1(2+5)n+11+(n+1)(3+5))



That's all.


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