Question 673220
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Hi,
The second and fifth terms of a geometric series are -15 and 405 respectively. 
 {{{a[2] = a[1](r)^1 = -15}}}  r = {{{-15/a[1]}}}
 {{{a[5] = a[1](-15/a[1])^4 = 405}}} &#8658;  {{{(-15)^4/405 = a[1] = 5}}}  and r  = -3
{{{S[n] = 5((1-(-3)^n)/(1-(-3)))}}}
{{{S[9] = 5((1-(-3)^9)/(4)))}}}= 24605