Question

Determine a soma dos 5 primeiros termos da P.G. (2, -6, 18,...)

Answer 1

a1=2
razão=6/2=3
n=5

$sn= \frac{a1.( q^{n}-1) }{q-1} = s5= \frac{-2.( 3^{5} -1)}{3-1} = s5= \frac{-2.(243-1)}{2} = s5= \frac{-2.242}{2} = s5= \frac{-486}{2} = s5=-243$