Question

Use the formula to evaluate the series 3-9+27-81+...-ae

Answer 1

( -4920)

Explanation:

we see that the first term is 3 and the common ratio between the succeeding terms is -3. so to solve for the sum of the first 8 terms

Sum = (a1)(1 – r^n) / (1 – r)

and substituting the known terms,we got

Sum = (3)(1 – (-3)^8)/(1 - (-3)) = -4920

Then the answer = ( -4920)