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anonymous
 one year ago
Find the sum of the first 9 terms of the sequence.
2, 7, 16, 25, ...
anonymous
 one year ago
Find the sum of the first 9 terms of the sequence. 2, 7, 16, 25, ...

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anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Have you seen this sort of sequence before?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Okay, cool. Just to help me know how to approach the problem, what have you guys been studying in class recently?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0I don't really understand how to find the sum of a sequence though

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Okay, I can help you with that! First of all, I think in this case we've got an arithmetic sequence rather than a geometric one, since we're adding (or subtracting) to get from one number to the next, rather than multiplying (or dividing).

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0There's a (magic) formula to find the sum of an arithmetic sequence. Would you like me to just remind you of the formula, or would you like to see where it comes from?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0u find the pattern between the numbers given and then continue the sequence like for this problem the pattern is u subtract 9 u keep doing that until u have nine terms counting the ones u already got and the add them all together

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0What @Player_2 suggested is one possible way, but it's not the fastest. Imagine if you had to add up 100 numbers rather than 9: it would take forever if you did it onebyone!

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0so then what's the "magic" formula

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Okay I was going to type out an expanation, but actually I think it'll just be faster if you watch this Youtube video. It's 7 minutes long, which is less time than I'd spend explaining it :) Here's the link: https://youtu.be/Uy_L8tnihDM

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0(If you don't have headphones/speakers then I can explain, of course  let me know if you prefer that option!)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0okay thank you! in the mean time can you tell me how to find the sum?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0To be honest, I'll have to work out the formula myself :) You start watching the video, and I'll let you know once I've worked it out. Does that work for you?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0(Let's see if I beat the 7 minute video!)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Okay, I get \[n(\frac{ 2a+(n1)d }{ 2 })\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Hmm, 7 minutes. Looks like I pretty much tied with the video :P

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0so the n would be 9 right? what about the a or d

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Well, "a" is the first number, so 2 in your case.

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0And "d" is the difference between the terms, which is 9 (since you're subtracting 9 each time)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Does that make sense at all? :)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0yes perfect sense thank you!

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0No problem! If you get stuck on any similar problems, I find the Khan Academy website really useful. It'll show you a video explaining the idea, and then let you try exercises, and I think it even works through the answers if you get stuck! https://www.khanacademy.org/math/integralcalculus/sequences_series_approx_calc/calculusseries/v/formulaforarithmeticseries
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