序号项 等差数列等比数列 等差数列前n项和
1a1a1=a1a1=a1S1=a1
2 a2 a2=a1+d a2=k a1S2=2a1+d
3 a3 a3=a1+2d a3=k^2 a1 S3=3a1+3d
4 a4 a4=a1+3d a4= k^3 a1S4=4a1+6d
5 a5 a5= a1+4da5= k^4 a1S5=5a1+10d
... ..
n an an=a1+(n-1)dan=k(n-1)a1Sn=na1 + 0.5n(n-1)d
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