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C1 Sequences and series

I am stuck on some C1 questions on Sequences and series.
Find how many terms of the following series are needed to make the given sum:
2+8+11+!4+...=670
Questions like these I've attempted however it seems, like in the example, I'd need a calculator to find the answer... any help?
How am I supposed to go about doing this?
You don't need a calculator. You have the first term, the common difference (although the series you gave as an example isn't an arithmetic series) and the sum, you just need to plug it into the formula and solve for n. You might need to do some long multiplication but you definitely don't need a calculator.
Original post by Chlorophile
...

How are we supposed to work out that the square root of 16129 is 127?
I cannot factorise it so I used the formula... :/ Help :smile:
Original post by MathMeister
How are we supposed to work out that the square root of 16129 is 127?
I cannot factorise it so I used the formula... :/ Help :smile:


Is this from the Edexcel C1 book? I seem to remember there being a question which asked you to root something ridiculous. In the actual exam, the questions will work out nicely. I've done all of the C1 papers for the last 5 years or so and there's never been anything like that. You definitely won't need to work out the root of a number like that in an actual exam.
Original post by Chlorophile
Is this from the Edexcel C1 book? I seem to remember there being a question which asked you to root something ridiculous. In the actual exam, the questions will work out nicely. I've done all of the C1 papers for the last 5 years or so and there's never been anything like that. You definitely won't need to work out the root of a number like that in an actual exam.

I suppose it wouldn't matter much anyway, because 97+% of people wouldn't get the last marks.
Original post by MathMeister
I suppose it wouldn't matter much anyway, because 97+% of people wouldn't get the last marks.


It's definitely possible to work out the square root of 16129, it shouldn't take you too long with a bit of trial and error. But still, it's not going to happen in an exam.
Original post by Chlorophile
It's definitely possible to work out the square root of 16129, it shouldn't take you too long with a bit of trial and error. But still, it's not going to happen in an exam.

https://www.youtube.com/watch?v=RbtgcMCkMGY :smile:
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davros
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Original post by Chlorophile
Is this from the Edexcel C1 book? I seem to remember there being a question which asked you to root something ridiculous. In the actual exam, the questions will work out nicely. I've done all of the C1 papers for the last 5 years or so and there's never been anything like that. You definitely won't need to work out the root of a number like that in an actual exam.



Original post by MathMeister
I suppose it wouldn't matter much anyway, because 97+% of people wouldn't get the last marks.


I believe some C1 textbooks contain questions from the old P1 exam where calculators were allowed. You won't get a question asking you to do this in C1 so don't worry!

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