∑k=0n(−1)n⋅(nk)⋅mm+k=(m+nn)−1\sum_{k=0}^n(-1)^n\cdot\binom nk\cdot\frac m {m+k}=\binom{m+n}n^{-1}∑k=0n(−1)n⋅(kn)⋅m+km=(nm+n)−1
