Number Stairs

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Introduction:

The topic which I have been given for my GCSE mathematics coursework, is “Number Stairs”. Therefore this leads mainly to the two topics “sequences” and “algebra”.

In this investigation I am going to examine the number steps in different positions, .  For part one of my assignment I will use a 10 – by –10 grid and investigate the effect of different size number steps.  I will find out the nth term formula for the number steps.  I will solve this using both algebraically and numerically methods. I will refer to the number in the bottom left hand corner.

Then going on for the second part of my assignment I will use different size number grids and also use different shapes e.g. T shape. The number which I refer to for my nth term will depend on the kind of shape that it is.

 For this first part of my coursework I will be using a 10 – by – 10 grid, which is given to investigate the number steps to find the formula for different number steps.  My grid is shown below:

2 step stair:

I will firstly go about investigating the 2-step stair numerically, but before I do that I need to find the total of  at least seven steps. I will work out the total of these steps then I will find the formula for these. I am going to start at number 1 and move from left to right.

Position One :

Total of position 1:

1+2+11 = 14

Position Two :

Total of position 2:

2+3+12 = 17

Position Three :

Total of position 3:

3+4+13 = 20

Position Four :

Total of position 4:

4+5+14 = 23

Position Five :

Total of position 5:

5+6+15 = 26

Position Six :

Total of position 6:

6+7+16 =  29

Position Seven :

Total of position 7:

7+8+17 = 32

Now that I have found out the totals of the first seven steps, I will be able to find the formula numerically for the 2-step stair:

nth term:

Rule          = +3

nth Term    = 3n+b

1st term  14= 3(1) +b

              14= 3+b

                b= 14-3

                b= 11

nth term      = 3n+11

Now I have worked out the formula numerically and also by using the value of position 1 and also by finding the difference. I have both times got the same formula 3n+11. Now I will see if this gives me the value of position 5.

Formula = 3n+11

Position 5 = 3 x 5 + 11 = 26

This is correct as in the total for position 5, which I worked out previously and I got the answer 26. This shows me that I have got the right formula as it works.

I’m now going to find out the formula algebraically and see if I get the same formula. If they both mach then it is correct.

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1+10 =11

n+n+n = 3n

End formula =3n+11

After finding my formula algebraically as well I can see that the formula should be correct. However just to make sure I will test the formula using 3 different numbers.

2 step stair : Testing

By using my formula 3n+11 I’m going to test this formula in three different positions referring to the number in the left hand corner.

I am firstly going to test the position 27 on a two step stair in a

10 – by – 10 ...

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