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Maths series help

Help on this seq and series q

I don’t get how to get part a because when I did it I did the sum of the first using this equation as it’s geometric

Sn= a(1-r^n) / 1-r
But a is the first term and it’s given as k=0
When I sub k equals zero into k cubed I get 0 as the first term therefore a=0
Now when I sub a=0 into geometric series sum equation shown above… I get 0 but that isn’t correctIMG_2273.jpegIMG_2274.jpeg
(edited 10 months ago)
Reply 1
Thats not geometric. A geometric would be ar^k. Its cubic, so k^3
Reply 2
Original post by mqb2766
Thats not geometric. A geometric would be ar^k. Its cubic, so k^3

Is it arithmetic ???
I don’t get why it’s not geometric because geometric is a sequence that times right?
I mean it’s
K x k x k
(edited 10 months ago)
Reply 3
You really should have covered basic geometric, arithmetic (linear) and quadratic sequences at gcse. This is cubic as its k^3, whch is pretty much the definition of a basic cubic. A geometric would go
a, ar, ar^2, ar^3, ...
and the summation/sequence index would be on the exponent, not the base.
Reply 4
Original post by mqb2766
You really should have covered basic geometric, arithmetic (linear) and quadratic sequences at gcse. This is cubic as its k^3, whch is pretty much the definition of a basic cubic. A geometric would go
a, ar, ar^2, ar^3, ...
and the summation/sequence index would be on the exponent, not the base.


We didn’t do GCSEs because of covid… and we got topic lists of what to revise… so that’s why I don’t know how to do it, sorry.thanks for the help
Reply 5
This is easier than you think. The difference between the sum of n terms and the sum of (n-1) terms is just the final nth term.
Reply 6
Original post by Matureb
This is easier than you think. The difference between the sum of n terms and the sum of (n-1) terms is just the final nth term.


Thank you, it very kind of you for not judging my ability

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