I'm having trouble coming up with a reason, conceptually, for why this identity is true. I know that the left hand side can be thought of as choosing a team of $k$ people from a group of $n$, including one team captain. However, I don't know how I can represent the right side in a similar respect.
2026-03-31 23:28:17.1774999697
Conceptual understanding for $k\binom{n}{k}=n\binom{n-1}{k-1}$
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