Rhind Mathematical Papyrus (8 of 8) / © 1979-2001 by Franz Gnaedinger, Zurich, fg@seshat.ch / www.seshat.ch

 

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RMP 56

 

The base of a pyramid measures 360 royal cubits and its height 250 royal cubits. Beginners calculate the sekad: how much does the slope recede on 1 royal cubit of height:

 

  half base / height  =  180 : 250  =  '2 '5 '50

 

  sekad  1 royal cubit x '2 '5 '50  =  5 '25 palms

 

Advanced learners may solve more demanding problems:

 

a) imagine a circle in the square of the base and calculate the circumference

 

b) transform the base into a regular octagon of about the same area; imagine a circle

in the square of the grid and calculate the circumference of that circle

 

c) transform the volume of the pyramid into a cube

 

Let us again consult the following number sequence:

 

  3  (plus 22)  25  47  69  ... 289  311  333  355  377

  1  (plus  7)   8  15  22  ...  92   99  106  113  120

 

The diameter of our circle measures 360 = 3 x 120 royal cubits. How long is the circumference? 3 x 377 = 1131 royal cubits. The area of the base measures 360 x 360 = 129,600 square cubits. Octagon of about the same area:

 

  side  164 royal cubits

 

  grid  116+164+116 by 116+164+116 royal cubits

 

  area (grid)  396x396 - 2x116x116  =  129,904 square cubits

 

  side length of grid  396 rc   diagonal  560 royal cubits

 

  diameter of inscribed circle  4 x  99  =   396 royal cubits

 

  circumference                 4 x 311  =  1244 royal cubits

 

Finally, the cube. The volume of the pyramid measures

 

  360 x 360 x 250 x '3  =  60 x 60 x 60 x 50 cubic cubits

 

while the edge of a cube of the same volume measures

 

  60 royal cubits x cube root of 50

 

How do we approximate the cube root of 50? By using the equation

 

  A x A x A  =  50 x B x B x B  plus/minus C

 

and looking out for numbers A and B that will keep C small:

 

   4 x  4 x  4  =  50 x  1 x  1 x  1   plus 16

  11 x 11 x 11  =  50 x  3 x  3 x  3   minus 19

  70 x 70 x 70  =  50 x 19 x 19 x 19   plus 50

 

The value 4 is too great:   4 x 4 x 4  =  64

 

The value '3 x 11 is a little too small:

 

  '3 x 11 x '3 x 11 x '3 x 11  =  '27 x 1331  =  49 plus ...

 

The value '19 x 70 is again a little too great:

 

  '19 x 70 x '19 x 70 x '19 x 70  =  50 plus ...

 

Pairs of such values generate further and better values:

 

  4  (plus 11)  15  26  37  48  59  70  81

  1  (plus  3)   4   7  10  13  16  19  22

 

  11  (plus 70)  81  151  221  291  361  431  501  571

   3  (plus 19)  22   41   60   79   98  117  136  155

 

  641  711  781  851  921  991  1061  1131  1201

  174  193  212  231  250  269   288   307   326

 

The value '307 x 1131 is the best approximation for the cube root of 50 (funny, we have already seen the number 1131), while the numbers 221 and 60 yield a simple solution to our problem:

 

  60 x cube root of 50  =  about  60 x 221 '60  =  221

 

A pyramid with a base of 360 royal cubits and a height of 250 royal cubits and a cube of the edge 221 royal cubits have nearly the same volume.

 

 

 

RMP 57 and 58

 

The base of a pyramid measures 140 royal cubits, the height  93 '3 royal cubits, and the sekad 5 palms 1 finger. Advanced learners may solve the following problems: Imagine a circle in the square of the base and another around the base: how long are the circumferences? Transform the area of the base into a circle: how long are the slopes of the pyramid? Imagine a hemisphere and a sphere in the frame of this pyramid: how long are the radii?

 

The base measures 140 royal cubits, the diagonal 198 royal cubits, and the average 169 royal cubits. If we regard these numbers as diameters of 3 circles, the circumferences measure:

 

  140 royal cubits  x   '7 x 22   =  440 royal cubits

  198 royal cubits  x  '99 x 311  =  622 royal cubits

  169 royal cubits  x '169 x 531  =  531 royal cubits

 

How can we transform the area of the base into a circle? We may use the value '7 of 22 and work with the following equation, looking out for good values of A and B which will keep C small:¨

 

  22 x A x A  =  7 x B x B  plus minus C

 

  22 x 22 x 22  =  7 x 39 x 39  plus 1

 

The numbers 22 and 39 provide a fine approximation for the square root of 're'. The pyramid base measures 140 royal cubits. I multiply this number by 22 and obtain 3080. Now I divide 3080 by 39 and obtain 79 minus '39 or practically 79. Hence, a circle of the radius 79 royal cubits and a square of the side 140 royal cubits have about the same area.

 

Now for the slope. The height measures '3 x 280 royal cubits, half the base measures '3 x 210 royal cubits, and the slope measures exactly '3 x 350 or 116 "3 royal cubits - according to the Sacred Triangle 3x70-4x70-5x70 = 210-280-350.

 

Now for the final answers: the radius of the imaginary sphere in the frame of this pyramid measures exactly 35 royal cubits, while the radius of the inscribed hemisphere measures exactly 56 royal cubits.

 

The imaginary sphere and hemisphere in the frame of the pyramid  symbolize the sun and the sky enclosed in the Primeval Hill.

 

 

 

RMP 59

 

Base and height of a pyramid measure 12 and 8 royal cubits. Let us imagine a wooden model of this pyramid:

 

  height  8 fingers   base 12 fingers

 

  half base  6 fingers  or  3 x 2 fingers

  height     8 fingers  or  4 x 2 fingers

  slope     10 fingers  or  5 x 2 fingers

 

This pyramid is again defined by a Sacred Triangle, so let me call this type of a pyramid a 'Sacred Pyramid'.

 

The surface of the model (base and four faces) measures 384 square fingers. How much is the volume? 384 cubic fingers.

 

The radius of the inscribed sphere measures exactly 3 fingers, while the distance from the center of the sphere to a corner of the base measures exactly 9 fingers (quadruple 3-6-6-9).

 

Now let us calculate the volume of a sphere of the diameter 9 fingers. Using the value '81 x 256 for 're’ we again obtain 384 cubic fingers. This generates a pretty formula: A square of the side 8 units and a circle with a diameter of 9 units have nearly the same area; a Sacred Pyramid with a height of 8 units and a sphere with a diameter of 9 units have nearly the same volume

 

 

 

RMP 60

 

Imagine a cone. The diameter of the base measures 15 royal cubits, and its height measures 30 royal cubits. Calculate the volume of the cone. Then imagine a sphere of the same diameter, 15 royal cubits. Calculate the volume of the sphere, using the same value for re (e.g. '15 of 47). The cone and the sphere have exactly the same volume.

 

 

 

 

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