geometric progression! HELP

a=1st term, n=no. of terms, r=common ration, L= last term

````1. r = -4, n = 6, S = -1.819; find a

``````2. a = 8, r = 3/2, S = 2059/8; find n

````````3. a = 3, r = 2/5, S = -609/125; find L

by naicarlz1

what's s? sum?

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