An arithmetic sequence $u_1, u_2, u_3, \dots$ has $u_1 = 1$ and common difference \(d \neq

Question

An arithmetic sequence $u_1, u_2, u_3, \dots$ has $u_1 = 1$ and common difference $d \neq 0$. Given that $u_2, u_3$ and $u_6$ are the first three terms of a geometric sequence, find the value of $d$. Given that $u_N = -15$ determine the value of $\sum_{r=1}^{N} u_r$.

Accepted Answer

(a) $d=-2$ (b) $-63$

AP, GP and Sigma-notation

AP, GP and Sigma-notation

Solution:

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