Question

Find the sum of the first six terms of a geometric series in which a1 = 4 and r = -3: A. 729 B. -729 C. -728 D. 728 plz help

Answer 1

Answer:

C

Step-by-step explanation:

The sum to n terms of a geometric sequence is

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

Here a₁ = 4 and r = - 3, thus

$S_{6}$ = $\frac{4((-3)^6-1)}{-3-1}$

    = $\frac{4(729-1)}{-4}$ = - (729 - 1) = - 728 → C