数列求和公式(n-4)(n-3)(n-2)(n-1)nb^5+5X(n-3)(n-2)(n-1)nb^4+5X4X(n-2)(n-1)nb^3+5X4X3X(n-1)nb^2+5X4X3X2Xnb^1+5X4X3X2X1像这种数列非等比,也非等差,如何求得求和公式?

Question

数列求和公式
(n-4)(n-3)(n-2)(n-1)nb^5 +
5X(n-3)(n-2)(n-1)nb^4 +
5X4X(n-2)(n-1)nb^3 +
5X4X3X(n-1)nb^2 +
5X4X3X2Xnb^1 +
5X4X3X2X1
像这种数列非等比,也非等差,如何求得求和公式?

Answer 1

x1(n) =(n-4)(n-3)(n-2)(n-1)nb^5= [b^5/6][ (n-4)(n-3)(n-2)(n-1)n(n+1) - (n-5)(n-4)(n-3)(n-2)(n-1)n]S1(n)= x1(1)+x1(2)+...+x1(n)= [b^5/6].(n-4)(n-3)(n-2)(n-1)n(n+1)x2(n) = 5(n-3)(n-2)(n-1)nb^4= b^4[(n-3...