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 correct

(edited 12 months ago)

Reply 1

mqb2766

21

Thats not geometric. A geometric would be ar^k. Its cubic, so k^3

Reply 2

Alevelhelp.1

OP

15

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 12 months ago)

Reply 3

mqb2766

21

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

Alevelhelp.1

OP

15

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.