In the equal ratio sequence an, a1 + a3 = 4, A2 + A9 = 8, find S8

In the equal ratio sequence an, a1 + a3 = 4, A2 + A9 = 8, find S8


Let A1, D, a1 + A1 + 2D = 4, a1 + D + A1 + 8D = 8, the simultaneous solution of the two equations is d = 4 / 7, A1 = 10 / 7, so S8 = 8 * 10 / 7 + 8 (8-1) * 4 / 2 * 7 = 192 / 7



In the equal ratio sequence {an}, (1) if A1 = 1, A9 = 256, find an


a9=a1q^8
256=q^8
q=±2
When q = 2
an=a1q^(n-1)
=2^(n-1)
When q = - 2
an=a1q^(n-1)
=(-2)^(n-1)

Elden Ring Premiere

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