Question: How to prove the combinatorial identity with Maple?

How to prove that 

sum(binomial(n, r)*binomial(k+r, n), r = 0 .. n) = sum(binomial(n, r)*binomial(k, r)*2^r, r = 0 .. n)?

Maple calculates the LHS and RHS, but I cannot compare these with Maple for each n::posint and each k::posint s. t. k>= n. The question was asked in Mathematics SE. I don't understand whether it is answered there.

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