Hello, I've tried these problems out already, I'm just a little stuck. I appreciate all your help. Thanks.

(Also, if you can explain how you came up with the answer, that would also be great so that I can learn), Thanks much.

1.

What is the sum of the first eight terms of the series?

(−500)+(−100)+(−20)+(−4)+(−0.8)+...

Round the answer to two decimal places if necessary.

−996.09

−625

−624.99

−623

2.

What is the sum of the first 7 terms of the series −3+6−12+24−... ?

Guest Apr 9, 2018

#1**+1 **

1. First eight terms ..... (−500)+(−100)+(−20)+(−4)+(−0.8)+...

The common ratio is (1/5)....the sum, S, is given by :

S = First Term [ 1 - common ratio^8] / [ 1 - common ratio ] =

S = -500 [ 1 - (1/5)^8] / [ 1 - 1/5] = -[ 624 + 624/625 ] ≈ -624.99

2. What is the sum of the first 7 terms of the series −3+6−12+24−... ?

The common ratio is -2

The sum, S, is given by :

S = -3 [ 1 - (-2)^7 ] / [ 1 - (-2) ] = -129

CPhill
Apr 9, 2018