9.1-3 – Sequences & Series | Mrs. Corricelli's BLOG

9.1-3 – Sequences & Series

Apr 26th, 2011 by corricelli

Please use this page to post questions about sections 9.1-9.3.

5 Responses to “9.1-3 – Sequences & Series”

Michaela Celella says:

April 26, 2011 at 7:54 pm

hey guys,
so I’m having a lot of trouble figuring out 121. I keep plugging it into the formula and I’m not getting the answer I should be. I’m finding the 1st term with multiplying 50 by the compound interest formula (1+(.05/12))^12*20 and then I’m trying to use the sum of a finite series formula in the book A = first term((1-r^n)/(1-r)) I’m plugging .05 in for r and it doesn’t make much sense. Help?

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Samantha Arsenault says:

April 26, 2011 at 9:17 pm

Michaela, I keep using the formula also and for some reason I keep getting 0? are you getting a number?

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Jeff M. says:

May 8, 2011 at 4:47 pm

For the Sierpinski Triangle activity for homework this weekend, for 4A, does it sound right that the common difference is 3/2^n, where n is the stage? I might be looking at the problem wrong.
To find the formula, I would use the Sum of a Finite Arithmetic Sequence: Sn = n/2 (a1+an), but to find An, I would need a common difference. 3/ 2^n satisfies it whenever I try it, but it sounds weird.

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Mawra Malik says:

May 8, 2011 at 5:28 pm

Jeff, I am kind of confused about the same problem. For 4A, its asking us to find the sum of the lengths of the nonoverlapping segments at Stage 10.

In order to see a pattern, I listed the sum of the lengths of nonoverlapping trianges from Stage 1-4 so far and I’m looking for the pattern…but im confused….here, this is what I did:
Stage 1: 1 + 1 +1 = 3
Stage 2: Stage 1 + 3(1/2) = 3 + (3/2) = 9/2
Stage 3: Stage 2 + 3(1/4) = 21/4
Stage 4: Stage 3 + 3(1/8) = 45/8
and so on…..

I tried to find a common ratio, but it doesn’t work? I understand though that Stage 10′s sum is going to be Stage 9 + the formula we derived for 3B. But I don’t know how to write that out?

Can any one help please?

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Mawra Malik says:

May 8, 2011 at 5:54 pm

Never mind, I looked at it again….and Jeff, you are right that the formula used will be finite geometric series. In order to use the formula, it’s important to know g1, r, and n. Well g1 is the sum of the length of the triangle in Stage 1 which is 1 + 1 + 1 = 3. n, in this problem, is going to be 10, as we are finding the sum at stage 10. r is 1/2 (look at Question number 3). So g1 = 3. n = 10. r = 1/2. Plug it into the finite geo. series fomula and you will get the answer.

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