I want to keep posting on SEQUENCES, not to distract but rather to keep us thinking new thoughts- kind of brain snacks to keep us thinking creatively and maybe see things in a new way, and HOPEFULLY find a sewuence or a key. (brainfood below)
A RULE:
A Sequence usually has a Rule, which is a way to find the value of each term.
Example: the sequence {3, 5, 7, 9, …} starts at 3 and jumps 2 every time:
{3, 5, 7, 9, …}
As a Formula
Saying "starts at 3 and jumps 2 every time" is fine, but it doesn't help us calculate the:
10th term,
100th term, or
nth term, where n could be any term number we want.
So, we want a formula with "n" in it (where n is any term number).
So, What Can A Rule For {3, 5, 7, 9, …} Be?
Firstly, we can see the sequence goes up 2 every time, so we can guess that a Rule is something like "2 times n" (where "n" is the term number). Let's test it out:
Test Rule: 2n
n Term Test Rule
1 3 2n = 2×1 = 2
2 5 2n = 2×2 = 4
3 7 2n = 2×3 = 6
That nearly worked … but it is too low by 1 every time, so let us try changing it to:
Test Rule: 2n+1
n Term Test Rule
1 3 2n+1 = 2×1 + 1 = 3
2 5 2n+1 = 2×2 + 1 = 5
3 7 2n+1 = 2×3 + 1 = 7
That Works!
So instead of saying "starts at 3 and jumps 2 every time" we write this:
2n+1
Now we can calculate, for example, the 100th term:
2 × 100 + 1 = 201