Question

Find the sum of the geometric series given a1=2, r=−3, and n=8.

Answer 1

Answer:

S₈ = - 3280

Step-by-step explanation:

The sum to n terms of a geometric series is

$S_{n}$ = $\frac{a_{}(r^{n}-1) }{r-1}$

Here a₁ = 2, r = - 3 and n = 8 , then

S₈ = $\frac{2((-3)^{8}-1) }{-3-1}$

   = $\frac{2(6561-1)}{-4}$

   = $\frac{2(6560)}{-4}$

   = $\frac{13120}{-4}$

   = - 3280

 

Answer 2

Answer:

Sum of the G.P is -3280

Step-by-step explanation:

Summation:

${ \bf{sum = \frac{a( {r}^{n }-1 )}{r - 1} }} \\ \\ { \tt{sum = \frac{2( { { - 3}^{8 } -1)} }{ - 3 - 1} }} \\ { \tt{ = \frac{13120}{-4} }} \\ = -3280$