i have to prove that:(adsbygoogle = window.adsbygoogle || []).push({});

n

sum [C(n,k)]^2=C(2n,n)

k=0

i have in my text a hint that i need to use:

(1+x)^n(1+x)^n=(1+x)^2n

but i got that:

n 2n

sum [C(n,k)]^2= sum [C(2n,k)]

k=0 k=0

how do i get out of this mess?

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# Summation problem

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