Question

Using:
\[\large \sum\limits_{r=0}^{n} \binom{n}{r}rx^{r} =nx(1+x)^{n-1}\]
Show that:
\[\large \sum\limits_{r=0}^{n} \binom{n}{r}
r^{2} = n(n+1)2^{n-2}\]

Answer 1

@lgbasallote

Answer 2

can you see the latex?

Answer 3

yes..but it's an error

Answer 4

noo.. there is something wrong with it; i cant even type it in the equation editor thing

Answer 5

refresh?

Answer 6

there is an extra } in the middle o:

Answer 7

take derivative of first one

Answer 8

@lgbasallote: Try it; good luck!

Answer 9

then let x=1

Answer 10

lol i know..this question is for @lgbasallote but looks like he is hiding

the edit buttom worked; thank you!

Answer 11

@apoorvk