【简答题】Parts Time Expressions Tony’s Steps toward Success 1~10 one evening during the Great Depression 11~13 summer passed into fall 14~16 one day 17~21 a year or two passed 22~27 after about two years 28~...
【简答题】规定A x m =x(x-1)…(x-m+1),其中x∈R,m为,且A x 0 =1,这是排列数A n m (n,m是,且m≤n)的一种推广. (1)求A -15 3 的值; (2)排列数的两个性质:①A n m =nA n-1 m-1 ,②A n m +mA n m-1 =A n+1 m .(其中m,n是)是否都能推广到A x m (x∈R,m是)的情形?若能推广,写出推...