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1. Good morning,

Please could anyone show me how to work out the nth term using this sequence

10, 40, 90, 160, 250
30 50 70 90
20 20 20

how do you actually get the answer 10n"

nth= a+(n-1)+half(n-1)(n-2)c

any help would be very much appreciated I have been trying to this since friday
2. clearly the nth term is 10n²

I dont know why you are trying to do it in dn(a-d) form
3. (Original post by GeneralGrievous)
clearly the nth term is 10n²

I dont know why you are trying to do it in dn(a-d) form

because i was tolD to
4. the thing is gina, you only use dn(a-d) when it's an arithmetic progression - ie the numbers go up linearly by a set amount each time.

like 1, 3, 5, 7.

once you have the amount going up varying and not fixed, it is no longer an arithmetic progression, and you can't use the formula you were given.
5. Thank you now what about the other equatation? I ahve come this far

a+(n-1)+half(n-1)(n-2)c
10+(n-1)30+half(n-1)(n-2)20
10+30n-30+10(n-1)(n-2)20
10+30n-30+10(n"-1n-2)20
10+30n-30+10n"-10n-20+20 I know the answer is 10n"

But how did I get it from the above

Thanks

Gina

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