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等差數列:Sn=(a1+an)n/2 Sn=n(2a1+(n-1)d)/2;(d為公差)Sn=An2+Bn;A=d/2,B=a1-(d/2)等比數列:Sn=n×a1(q=1)Sn=a1(1-q^n)/(1-q)=(a1-an*q)/(1-q)(q≠1)S∞=a1/(1-q)(n->∞)(|q|
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