1(1−x)n+1=∑i=0∞Cn+inxi\dfrac{1}{(1-x)^{n+1}}=\sum\limits_{i=0}^\infty C^n_{n+i} x^i(1−x)n+11=i=0∑∞Cn+inxi
生成函数的内容，然鹅菜鸡我推不出来/kk
