Saturday, May 23, 2009

[squaring the circle] and other gems


Squaring the Circle

Squaring the circle is one of the three great problems of Classical Geometry, along with the trisection of the angle and the duplication of the cube.

Since 1800 B.C. mathematicians have worked on the problem of constructing a square equal in area to that of a given circle. Whether or not this is possible depends, of course, on what tools you allow yourself. Plato insisted that the problem be solved with straightedge and compass only.

To achieve this requires constructing a length equal to Pi times the square of the radius of the circle. Thus when Lindemann proved in 1882 that Pi is transcendental (not the root of any polynomial with rational coefficients) he effectively proved that the construction was impossible with only straightedge and compass.



Dimensions of The Great Pyramid

Some interesting mathematics is associated with The Great Pyramid of Cheops. Here are its dimensions in Royal Cubits, the measurements employed at the time:

(A Royal cubit is equal to about 20.62 inches or 0.5239 metres and was the distance from elbow to fingertip of the Pharoah.)

a] The area of a circle = Pi R2 b] The circumference of a circle = 2 Pi R
Bear in mind the value of Pi = 3.14 to two places and keep the figure 2 also in mind.

Task 1: Double the base length of the pyramid and divide by the height.

Task 2: Take the perimeter of the base and divide by the height, then halve that. See anything interesting? OK, so what does Pi have to do with a linear polygon?

Task 3: Take the distance when Earth is closest to the Sun (perihelion): 147x106 km and translate it into Royal Cubits. What is the number x 109 ?

Euclid said:

A straight line is said to have been cut in extreme and mean ratio when, as the whole line is to the greater segment, so is the greater to the less.

This means that if I divide a line into two and when the ratio of the whole line to bigger piece is the same as for the bigger to the smaller, then we have The Golden Ratio.



This is translated into a number: 1.6180

Task 4: Divide the "slant height" of the pyramid (356 RC) by its "half base" (220 RC) and what figure do you get?

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