Hidden faces

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Hidden faces

Introduction

I am investigating the number of hidden faces for different rows of cubes. When the cubes are placed on a table, you cannot touch them or move them however you may move the table around.

Examples

When a cube is placed on a table only 5 of the faces can be seen. So 1 face is hidden.

Figure 1 on the dotted paper shows this.

When five cubes are placed on a table only 17 faces can be seen. So 13 faces are hidden.

Figure 2 on the dotted paper shows this.

Part 1

I will tackle this problem by investigating different numbers of cubes. These cubes that I'll be using are 1 cube, 2 cubes, 3 cubes, 4 cubes and 5 cubes. These cubes are shown on the dotted paper. This method is sensible because using the number of cubes I'd be using could lead to finding a formula easily.

Number of cubes

Number of faces seen

Number of faces hidden

Total number of faces

5

6

2

8

4

2

3

1

7

8

4

4

0

24

5

7

3

30

Patterns

Patterns that I noticed was in the column 'Number of faces seen' that when a cube has 5 faces seen, 2 cubes has 8 faces seen. Three cubes have 11 faces seen, 4 cubes have 14 faces seen and 5 cubes has 17 faces seen. Between each cube is a gap of 3. This could help me with my finding of a formula. I also noticed that in the column 'Number of faces hidden' that when a cube has 1 face hidden, 2 cubes have 4 faces hidden. Three cubes have 7 faces hidden, 4 cubes have 10 faces hidden and 5 cubes has 13 cubes hidden. Between each cube is a gap of 3. This could help me with my finding of a formula. Finally I noticed in the column 'Total number of faces' that when a cube has a total of 6 faces, 2 cubes has a total of 12 faces. Three cubes have a total of 18 faces, 4 cubes have a total of 24 faces and 5 cubes have a total of 30 faces. Between each cube is a gap of 6. This could help me with my finding of a formula. These are all the patterns that I have noticed.
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Formula

H = Number of hidden faces

N = Number of cubes in the row

The formula that I have found for the number of hidden faces for different rows of cubes is H = 3N - 2. The 'h' in the formula stands for the number of hidden faces. The 'n' in the formula stands for the number of cubes that is in the row. So the formula means 3 multiplied number of cubes in row subtract 2. I'll prove that this formula works by using 5 cubes. So 5 multiplied by 3 equals ...

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