how to do this series question | Revision Server | Page 1

slow linden Jan 30, 2024, 7:34 PM

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which part?

quasi pike Jan 30, 2024, 7:34 PM

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ii

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Not sure about the 2n+1 part

slow linden Jan 30, 2024, 7:35 PM

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its definition not a typo?

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jus checking

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bc usually the expression is always in terms of r

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wait it cant even be a typo bc it would cancel out

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lemme try the q and ill get back to you

quasi pike Jan 30, 2024, 7:36 PM

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Yeah just what I was about to say

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Alr thanks

slow linden Jan 30, 2024, 7:39 PM

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treat 2n + 1 as a constant

quasi pike Jan 30, 2024, 7:39 PM

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Also lmk what you get on part a

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Ok lemme try it

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Just write a K?

slow linden Jan 30, 2024, 7:40 PM

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nah just think about it as if its a constant

quasi pike Jan 30, 2024, 7:40 PM

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?

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Show workings?

slow linden Jan 30, 2024, 7:40 PM

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alr lemme finish

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icl this question is cooked 💀

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what i got doesnt factorise into the form

quasi pike Jan 30, 2024, 7:46 PM

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Ok lemme try stay there

proper oak Jan 30, 2024, 7:48 PM

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slow linden what i got doesnt factorise into the form

Is this for ii

quasi pike Jan 30, 2024, 7:52 PM

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Yeah

proper oak Jan 30, 2024, 7:53 PM

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I got an answer dont know if its right

quasi pike Jan 30, 2024, 7:53 PM

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Workings?

proper oak Jan 30, 2024, 7:54 PM

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But you are summing up the 2n+1 bit n+1 times from r=0 to n

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So its Σr² - 2Σr + (n+1)(2n+1) you can simplify that and factorise

quasi pike Jan 30, 2024, 7:56 PM

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Pffff I’m confused

proper oak Jan 30, 2024, 7:56 PM

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Which bit

quasi pike Jan 30, 2024, 7:57 PM

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1st kind

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What to do when n=0?

proper oak Jan 30, 2024, 7:58 PM

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You can still use the standard results for r and r² since adding 0 doesnt change them

quasi pike Jan 30, 2024, 7:58 PM

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Oh I see

proper oak Jan 30, 2024, 7:58 PM

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The 0 affects the constants

quasi pike Jan 30, 2024, 7:58 PM

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I get the r^2 and -2r but not next bit

proper oak Jan 30, 2024, 7:59 PM

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Say for example Σ(r+5) from r = 1 to 5

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How many times in total do you add 5

quasi pike Jan 30, 2024, 8:01 PM

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5

proper oak Jan 30, 2024, 8:01 PM

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Yes since there are 5 terms you do 5(5) = 25 in total

quasi pike Jan 30, 2024, 8:01 PM

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Yes

proper oak Jan 30, 2024, 8:01 PM

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So in this case with the 1, there are n+1 terms in total

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So we add on n+1

quasi pike Jan 30, 2024, 8:02 PM

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proper oak So in this case with the 1, there are n+1 terms in total

Don’t get

proper oak Jan 30, 2024, 8:02 PM

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If its Σ(r+5) from r = 1 to n how many times do u add 5

quasi pike Jan 30, 2024, 8:03 PM

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5…

proper oak Jan 30, 2024, 8:03 PM

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No you add 5 for each term

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1+5 + 2+5 + 3+5 … n+5

quasi pike Jan 30, 2024, 8:04 PM

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Ok yeah

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But I thought it would be 5n?

proper oak Jan 30, 2024, 8:04 PM

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Ye so that summation can be rewritten as Σr + 5n

quasi pike Jan 30, 2024, 8:05 PM

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Ok yeah

proper oak Jan 30, 2024, 8:05 PM

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From r=0 to n how many terms are there

quasi pike Jan 30, 2024, 8:05 PM

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6

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N+1

proper oak Jan 30, 2024, 8:05 PM

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Ye

quasi pike Jan 30, 2024, 8:05 PM

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Ok I see

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What was your final answer to the q so I can check when I’m done?

proper oak Jan 30, 2024, 8:06 PM

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1/6(n+1)(n+6)(2n+1)

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I will check my answer tho

quasi pike Jan 30, 2024, 8:11 PM

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Still can’t do it lol

proper oak Jan 30, 2024, 8:12 PM

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Ye im redoing it and it wont factorise lol

quasi pike Jan 30, 2024, 8:13 PM

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I got it

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Thanks for your help though buddy

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Have a great night

proper oak Jan 30, 2024, 8:16 PM

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Ye i got the same

#how to do this series question