求和(a-1)+(a²-2)+...+(a的n次方-n) (a≠0)
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求和(a-1)+(a²-2)+...+(a的n次方-n) (a≠0)
求和(a-1)+(a²-2)+...+(a的n次方-n) (a≠0)
求和(a-1)+(a²-2)+...+(a的n次方-n) (a≠0)
(a-1)+(a²-2)+...+(a的n次方-n) (a≠0)
=(a+a²+….a的n次方)-(1+2+…..n)
=a(1-a的n次方)/(1-a) - (1+n)n/2