Question

Prove that if m and n are positive integers:
1≤k≤n, then \[\sum_{i=0}^{k}(n choose i)(mchoosek-i)=(m+n choose k)\]

Answer 1

i don't know how to write those notation with ("n" the top and "i"under it)

Answer 2

can you draw the equation instead?

Answer 3

I am going to attach it.

Answer 4

Hope you are able to see it

Answer 5

Do you know what combinatorial proofs are?