1×Ck−10+2×Ck−11+…n×Ck−1n−11\times C_{k-1}^{0}+2\times C_{k-1}^{1}+\ldots n\times C^{n-1}_{k-1}1×Ck−10+2×Ck−11+…n×Ck−1n−1
怎么算？能不能给出详细过程谢谢
