# Thread: Geometric Series (Sum Formulas)

1. ## Geometric Series (Sum Formulas)

Ok, I have more of a technical issue here since I know how to calculate the sum of geometric series.

The question asked is: Find the sum of the following series: 3 + 3square root of 9 + 9... S7.

My question is, how is "3square root 9" entered into a calculator? Note that the "3" is not a cubed root... it is just on the left-hand side of the square root sign. I know that it has to equal 5.196... since r = the square root of 3 (the question provides this), but I just can't figure out how to enter this into my graphing calculator.

Thanks.

2. ## Re: Geometric Series (Sum Formulas)

Is this the series?

$\displaystyle \displaystyle 3+3\sqrt{9}+9+\cdots$

If so, is it geometric?

3. ## Re: Geometric Series (Sum Formulas)

Originally Posted by oryxncrake
Ok, I have more of a technical issue here since I know how to calculate the sum of geometric series.

The question asked is: Find the sum of the following series: 3 + 3square root of 9 + 9... S7.

My question is, how is "3square root 9" entered into a calculator? Note that the "3" is not a cubed root... it is just on the left-hand side of the square root sign. I know that it has to equal 5.196... since r = the square root of 3 (the question provides this), but I just can't figure out how to enter this into my graphing calculator.

Thanks.
Dear oryxncrake,

It depends on the graphing calculator that you use. So the best thing is to refer the manual of the calculator. What is the model of the graphing calculator that you use?

4. ## Re: Geometric Series (Sum Formulas)

Yes, that is the series and it is geometric.

5. ## Re: Geometric Series (Sum Formulas)

I am using the TI-83 Plus

6. ## Re: Geometric Series (Sum Formulas)

Originally Posted by oryxncrake
Yes, that is the series and it is geometric.
$\displaystyle \displaystyle 3+3\sqrt{9}+9+\cdots$

$\displaystyle \displaystyle 3+3\times 3+9+\cdots$

$\displaystyle \displaystyle 3+9+9+\cdots$

Is it geometric?

7. ## Re: Geometric Series (Sum Formulas)

$\displaystyle 3 + 3\sqrt{3} + 9 + ...$

is geometric. a "typo" maybe?

8. ## Re: Geometric Series (Sum Formulas)

3 + 3sqrt(9) is 3 + 3*3, so multiplier = 3; so 3,9,27,81...

9. ## Re: Geometric Series (Sum Formulas)

Originally Posted by skeeter
$\displaystyle 3 + 3\sqrt{3} + 9 + ...$

is geometric. a "typo" maybe?
Yep that looks a bit better!