$\sum_{r=0}^{40} {40 \choose r} (-1)^r {100-r \choose 40} = 1$
I have tried expanding, simplifying it. It doesn't work. Anyone has any ideas?
2026-03-28 11:32:14.1774697534
proof for $\sum_{r=0}^{40} {40 \choose r} (-1)^r {100-r \choose 40} = 1$
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