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universal-confusion

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Hi everyone, I'm new to these forums, so I've only just realized how much help they can be... I have some questions so please, don't hesitate to aid me in my time of need.

These are regarding geometric sequences and series. I'm supposed to be using S=a+ar^n/1-r where s=the sum of the terms

a=the first term

r= the common ratio

n=the # of terms

1.) How many generations must a person go back to have at least 1000 ancestors? (The sequence is supposed to go: 2+ 4+ 8+ 16+ ...) I know how to do it, I think, but the part that confuses me is where it says AT LEAST 1000. that means i can't use 1000 in the equation, right? because that's not the sum, that is just approx. the sum. ugh.

2.) The sum of the first two terms of a geometric series is 12 and the sum of the first 3 terms is 62. Find the first 3 terms of the series. I tried solving the equation for a then substituting it in so i only have one variable, but I got something like, r=r...

3.) The second term of a geometric series is 15 and the sum of the first 3 terms is 93. Find the first 3 terms of the series. I know this question will be using the same ideas as 2 but once again it doesn't seem to work the way I'm doing it.

These are regarding geometric sequences and series. I'm supposed to be using S=a+ar^n/1-r where s=the sum of the terms

a=the first term

r= the common ratio

n=the # of terms

1.) How many generations must a person go back to have at least 1000 ancestors? (The sequence is supposed to go: 2+ 4+ 8+ 16+ ...) I know how to do it, I think, but the part that confuses me is where it says AT LEAST 1000. that means i can't use 1000 in the equation, right? because that's not the sum, that is just approx. the sum. ugh.

2.) The sum of the first two terms of a geometric series is 12 and the sum of the first 3 terms is 62. Find the first 3 terms of the series. I tried solving the equation for a then substituting it in so i only have one variable, but I got something like, r=r...

3.) The second term of a geometric series is 15 and the sum of the first 3 terms is 93. Find the first 3 terms of the series. I know this question will be using the same ideas as 2 but once again it doesn't seem to work the way I'm doing it.

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