Number Grid Investigation.

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Number Grid Investigation

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Task.

My task is to use the box above to do the following things:

* Draw a box around 4 numbers.

* Find the product of the top left number and the right number within this box.

* Do the same with the top right and the bottom left numbers.

* Calculate the difference between these products.

* INVESTIGATE FURTHER...

This assignment is concerned with product differences in different size matrices for different sized grids.

Above is a 10 X 10 grid. We are trying to investigate product differences within this 10 X 10 grid. As you can see I have drawn a 2 X 2 grid inside the 10 X 10 matrix. To find the product difference I do:

Top left number X bottom right - top right X bottom left.

TL X BR - TR X BL

TL = Top left

BR = Bottom right

TR = Top right

BL = Bottom left.

The product difference I found was 10. This was anywhere on the grid where a 2 X 2 grid could be drawn.

To prove this I will take a 2 X 2 grid and use the above formula to work out the product difference. Below is the result of me picking a 2 X 2 grid from this 10 X 10 grid and calculating the product difference.

67

68

77

78

I did (67 X 78) - (68 X 77) = 10

This shows that the product difference is 10.

Below are two more examples to prove it will work anywhere on the grid.

42

43

52

53

I did (42 X 53) - (43 X 52) = 10

TL X BR - TR X BL

2

3

22

23

I did (12 X 23) - (13 X 22) = 10

TL X BR - TR X BL

I am now going to prove algebraically that in a 10 X 10 grid, with a 2 X 2 square the difference will always be 10.

X

X+1

X+10

X+11

( (x + 1) (x + 10) ) - x ( x + 11)

(x² + x + 10x + 10) - (x² + 11x)

(x² + 11x + 10) - (x² + 11x)

x² + 11x + 10 - x² - 11x

Difference = 10

This proves algebraically that the difference in a 2 X 2 square is 10.

What can be done now?

Brainstorm

* Vary the shape of box (square, rectangle)

* Vary size of grid (width, shape)

* Try different calculations.

* Use a different pattern of numbers.

Plan.

The above brainstorm explains the different approaches that can be taken in this investigation. Firstly I will vary the size of the box inside the 10 X 10 grid. I will then move my way through the different approaches constantly comparing and making notes on my findings.

Vary the shape of box

We have already worked out the Product difference of a 2 X 2 square within a 10 wide grid. This was always 10, I have used algebra to prove the 'always'.

I am now going to see what happens when I change the box size to a 3 X 3 square.

Here is a 3 X 3 square taken from a 10 wide grid:

37

38

39

47

48

49

57

58

59

So, the calculation that I did was: (TL X BR) - (TR X BL)

(37 X 59) - (39 X 57) = 40.

With the above calculation I discovered that for a 3 X 3 square within a 10 wide grid the product difference is 40.

I will now do another two examples to see if it is the same anywhere in the grid as the 2 X 2 was.

28

29

30

38

39

40

48

49

50

(28 X 50) - (30 X 48) = 40. This shows again that the product difference is 40.

6

7

8

26

27

28

36

37

38

(16 X 38) - (18 X 36) = 40.

The above examples show that the product difference of a 3 X 3 grid will always be 40 no matter where it is on the grid.

To prove this above statement I am now going to prove algebraically that the product difference will always be 40.

x

x +

x + 20

x + 22

((x + 2)(x + 20)) - x(x + 22)

(x² + 2x + 20x + 40) - (x² + 22x)

(x² + 22x + 40) - (x² + 22x)

Difference = 40.

Mini Conclusion

So far I have discovered that in a 2 X 2 square the product difference is always 10 and in a 3 X 3 square the product difference is always 40.

I will now try a 4 X 4 square within a 10 wide grid.

0 wide grids with a 4 X 4 square.

Again, I am going to use the formula: (TL X BR) - (TR X BL)

This is an example of a 4 X 4 box taken from a 10 wide grid:

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54

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57

64

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66

67

I then did:

(TL X BR) - (TR X BL)

(34 X 67) - (37 X 64) = 90.

90 is the product difference in a 4 X 4 square.

Mini prediction

I am presuming from my above predictions that any 4 X 4 square taken from this 10 wide grid will also show a product difference of 90.

Let's see...

I will now do another two examples to see if my prediction is correct.

24

25

25

27

34

35

36

37

44

45

46

47

54

55

56

57

(24 X 57) - (27 X 54) = 90.

66

67

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69

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96

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99

(66 X 99) - (69 X 96) = 90.

Both calculations show a product difference of 90.

I will now prove the above findings algebraically.

x

x + 3

x + 30

x + 33

((x + 3)(x + 30)) - x(x + 33)

(x² + 3x + 30x + 90) - (x² + 33x)

(x² + 33x + 90) - (x² + 33x)

Difference = 90.

What have we noticed so far?

Within a 10 wide grid:

2 X 2 squares product difference is 10.

3 X 3 squares product difference is 40.

4 X 4 squares product difference is 90.

Size of Square

2 X 2

3 X 3

4 X 4

Product Difference

0

40

90

I now need to attempt finding a formula connecting the size of the square inside the 10 wide grid.

Finding a formula for size of square inside 10 wide grid

Firstly I noticed that if you take the '0' of the product difference you are left with square numbers.
Join now!


, 4, 9 ...

So, I tried to find a way you could get the square numbers.

(2 - 1 = 1) X 10 = 10

The formula would be 10(width of square - 1)

I then tried, using this formula, in a 3 X 3 square.

10(3 - 1) = 20.

This was wrong as my intended answer was 40, not 20. I need to multiply the 10 by 4 somehow.

So, I squared the (3 - 1) to get 4.

10 (3 - 1)²

This worked. The ...

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