# recent gcse question - i can't work it out!

• November 7th 2007, 01:22 PM
becky.x12
recent gcse question - i can't work it out!
I am doing A level maths at the moment, but can't seem to work this out at all :S help would be much appreciated!!
It was to find a rule for this sequence:
when n=1, x=3
when n=2, x=6
when n=3, x=7
when n=4, x=-2

If you can help me, thank you! :)
Becky
• November 7th 2007, 01:38 PM
becky.x12
Sorry I don't mean to be rude, just thought I'd say please let me know as soon as possible because it's driving me mad lol!
Thank youuuu :)
• November 7th 2007, 02:06 PM
Soroban
Hello, Becky!

Quote:

Find a rule for this sequence: . $3,\:6,\:7,\:\text{-}2,\:\cdots$
There is no simple pattern to the sequence.
. . [If there is one, I've missed it.]

There is an infinite number of polynomial functions
. . that contain the four points: . $(1,3),\;(2,6),\;(3,7),\;(4,-2)$.

The simplest is a cubic: . $f(n) \:=\:-\frac{4}{3}n^3 + 7n^2 - \frac{26}{3}n + 6$