Transcript Sequences Revision

Sequences Revision
Saturday, 18 July 2015
Position to term rules
It is important to be able to find the number in a
sequence from its position in that sequence.
Example.
If we want to find the 100th term in the sequence
2, 6, 10, 14,18………
Do we need to keep adding 4, until we find the
100th number in the sequence!!
Any suggestions?
1,
2,
3,
4,
5 ……………….Position in sequence (n)
2, 6, 10, 14, 18 ………………. Common difference = 4
4, 8, 12, 16, 20………………. Numbers in 4 x table (4n)
To find numbers in sequence multiply position by 4 and take 2
nth Term = 4n – 2
100th term = (4 x 100) – 2
= 398
1,
2,
3,
4,
5 ……………….Position in sequence (n)
8, 13, 18, 23, 28 ………………. Common difference = 5
5, 10, 15, 20, 25………………. Numbers in 5 x table (5n)
To find numbers in sequence multiply position by 5 and add 3
nth Term = 5n + 3
100th term = (5 x 100) + 3
= 503
Example
Here is a sequence made from match sticks.
𝟔
Diagram 1
𝟏𝟏
𝟏𝟔
Diagram 2
Diagram 3
𝟐𝟏
(a) Draw the next diagram in the sequence.
(b) Write down the number of sticks used in each of the first four
diagrams.
𝟐𝟏
(c) Write down a formula connecting the number of sticks used and
the diagram number.
𝟓𝒏 + 𝟏