Prove (binomial)

[metru]

Prove:
\(\displaystyle C_{k - 3}^{k - 3} \cdot C_{n - k + 2}^2 + C_{k - 2}^{k - 3} \cdot C_{n - k + 1}^2 + C_{k - 1}^{k - 3} \cdot C_{n - k}^2 + \cdots + C_{n - 3}^{k - 3} \cdot C_2^2 = C_n^k\)

 

[Denis]

I proved it using a napkin at Burger King; sorry, lost the napkin :roll:

 

[jolly]

I proved it using a napkin at Burger King; sorry, lost the napkin :roll:

:lol: