cn=(2n+1)8∧(n-1)用错位相减法求和
问题描述:
cn=(2n+1)8∧(n-1)用错位相减法求和
答
letS =1.8^0+2.8^1+.+n.8^(n-1) (1)8S = 1.8^1+2.8^2+.+n.8^n (2)(2)-(1)7S = n.8^n -[1+8+...+8^(n-1) ]=n.8^n -(1/7)(8^n -1)S = (1/7)[ n.8^n -(1/7)(8^n -1) ]cn= (2n+1).8^(n-1)= 2[n.8^(n-1)] + 8^(n-1)Sn = c...