Question

1. Use the formula to evaluate the series -3 + 6 - 12 + 24 - ...-a.

Sn =
al(1-7)
1-1
In the formula for a finite series, a, is the first term, r is the common ratio, and n is the number of terms.

Answer 1

Sn =(-2)^n-1

Explanation:

hello :

the formula is : Sn = a (r^n-1)/(r-1)

in this exercice : a = -3 r= 6/-3 = -12/6 = 24/-12 = -2

so : Sn = -3 ((-2)^n-1)/(-2-1)

Sn =(-2)^n-1