ALGEBRA BEGAN IN IRAQ
("Life can only be understood backward, but must be lived forward", Sören Kierkegaard, Danish philosopher.)
I say it's no accident that the first society to advance in ASTRONOMY was the first to advance in ALGEBRA: BABYLONIA. We learn this in Mathematical Thought From Ancient to Modern Times, v. I, pp. 8-10, Morris Kline.

Babylon was situated in the area known as Mesopotamia (Greek for "between the rivers"). Mesopotamia was in the Near East in roughly the same geographical position as modern Iraq. Two great rivers flow through this land: the Tigris and the Euphrates. Along these two rivers lay many great trading cities such as Ur and Babylon on the Euphrates. Most of central Mesopotamia would have been desert except in the vicinity of the two rivers: the Tigris and the Euphrates which carry water to the area. These rivers formed the huge alluvial plain on which the agricultural prosperity of the region was built.

It was this area where Babylon was built. To the west of Mesopotamia stretches the Arabian desert. It is inhabited by nomads: the forerunners of the modern Bedouin. These nomads played a significant part in the history of Mesopotamia and of Babylon. Northern Mesopotamia encompasses the foothills of mountains of eastern Anatolia.

This is the area of Assyria. It has a wetter environment. This means crops could be grown partially without irrigation. Most of central Mesopotamia would have been desert except in the vicinity of the two rivers: the Tigris and the Euphrates which carry water to the area. These rivers formed the huge alluvial plain on which the agricultural prosperity of the region was built. It was this area where Babylon was built.

To the west of Mesopotamia stretches the Arabian desert. It is inhabited by nomads: the forerunners of the modern Bedouin. These nomads played a significant part in the history of Mesopotamia and of Babylon. To the east of Mesopotamia lay the land of Elam. Elam lay in present west Iran on the Zagros mountains. Central and southern Mesopotamia: the area south of modern Baghdad forms the area called Babylonia though it incorporates many other cities as well as Babylon. It was here where the conditions were correct because it had one commodity in huge amounts: clay.

Babylonian priests made ASTRONOMY in effect THE FIRST OF THE SCIENCES by devoting a period of 10,000 years to its development. This Near-Eastern record is unequaled in "Western" Science. Some historians of science date it back to Galileo, Tycho Brahe, Kepler and Newton. which would be less than 500 years. Even if we "date Rationality" back to the days of Thales and Pythagoras, this is only 2500 years -- one fourth the Babylonian record. And this record was made possible by advances in ALGEBRA.


Solving Quadratics

Problem. Solve x(x + p )= q.

Solution. Set y = x + p.

Then we have the system xy = q, y - x = p.

This gives

4xy + (y - x)2
(y + x)2 = p2 + 4q
x + y = (p2 + 4q)1/2
2x + p = (p2 + 4q)1/2
x = 1/2(-p + (p2 + 4q)1/2)
.

All three forms

x2 + px + q
x2 = px + q
x2 + q = px

are solved similarly. The third is solved by equating it to the nonlinear system, x + y = q, xy = q. Moreover, all three date back 4,000 years!

Solving Cubics

The Babylonians must have had extraordinary manipulative skills and as well a maturity and flexibility of algebraic skills.

Solving linear systems.

Solve: 2x/3 - y/2 = 500, x + y = 1800.

Solution: Select x' = y' such that x' + y' = 2x' = 1800.

So, x' = 900. Now make the model x = x' + d, y = y' + d.

We get

2/3(900 + d) - 1/2(900 - d) = 500
(2/3 + 1/2)d + 1800/3 - 900/2 = 500
7/6d = 500 - 150
d = 6(350)/7
.

So, d = 300 and thus x = 1200, y = 600.

Old Babylonian mathematicians were much taken with problems involving two unknowns and square roots, what we would term 'quadratic' problems. These problems usually involved finding lengths, widths or diagonals of rectangles. The simplest example would be a problem giving the sum or the length and width of a rectangle (or field) and its area. The problem is to find the length and the width. So we might read, 'Length plus width is 50. Area is 600. What are the length and the width?' In all of Old Babylonian mathematics, it is understood that the length is at least as large as the width.

A modern student would probably write down the formulas  l + w = 50 and lw = 600, solve the first as, say, w = 50 - l ,substitute for w in the second equation to get hw = l(50 - l) = 50 l - l2, and then solve the quadratic equation l2 - 50l - 600 - 0 for l using the quadratic formula to obtain l = 30, from which it follows that w = 20.

The Old Babylonian procedure was rather different.

First, it is important to note that Mesopotamian mathematics was largely algorithmic in style. That is, instead of writing down a formula and substituting particular values for the variables, Old Babylonian mathematicians concentrated onfollowing a particular procedure. The procedure for the type of problem given above was as follows:

  1. Take half the sum of the length and width (we'll call this thehalf-sum): 25
  2. Square the half-sum: 625.
  3. Subtract the area: 25
  4. Take the square root: 5.

Length is half-sum + square root: 30

Width is half-sum - square root: 20.

Another popular type of problem is where the student is given the difference of the length and the width as well as the area. So we would read, 'Thelength exceeds the width by 10. The area is 600. What are the length andthe width?' The procedure for this type of problem is very similar.

  1. Take half the difference of the length and width (the half-difference):5
  2. Square the half-difference: 25
  3. Add the area: 625
  4. Take the square root: 25
Length is square root + half-difference: 30

Width is square root - half-difference: 20.

Hundreds of these 'rectangular' problems are known. In many cases, just the problem is stated, but in others the procedure is given so that we can see how they solved the particular types of problems. Interestingly, we have no examples of the two basic types given above. They must have been considered too easy to bother writing them down. However, in the case of more complicated types of problems (such as being given the difference of the length and width and the area minus the square of the difference) the first step is to reduce the problem to one of the two standard types above and then solve it with the standard procedure.

The first major analysis of Babylonian rectangular problems was by Solomon Gandz in 1937, in a massive paper in Osiris. He divided Mesopotamian quadratic problems into nine types, o which the simple ones given above are Types I and II. In that paper, Gandz also speculated as to how the Babylonians derived their procedures and noted similarities between their approaches and the procedures of Diophantus, contrasting these with both the Arabic and modern approaches.

More complicated algebraic problems were transformed to simpler ones (showing implicit knowledge of THE BYPASS STRATEGY we cite in other files!).

Says Kline, "The Babylonians were able to solve special problems involving five unknowns in five equations. One problem, which arose in connection with the adjustment of astronomical observations, involed ten equations and ten unknowns, mostly linear.... Problems leading to a cube root also occurred. The modern formulation of such a problem would be: 12x = z, y = x, xyz = V, where V is some unknown volume. To find x here we must extract a cube root. The Babylonians calculated this root from [cube root tables they compiled]. They also did compound interest problems that called for finding the value of an unknown exponent." (LOGARITHMS! which we also take up elsewhere.)

Today, we use SYMBOLIC ALGEBRA to avoid confusion with the (English) language discussion of the mathematics. The ancient Babylonians sometimes achieved this effect by using Sumerian-Akkadian words.

Some of this "Babylonian algebra" was needed to treat inheritance.

Repeating my initial statement: It's no accident that the first society to advance in ASTRONOMY was the first to advance in ALGEBRA: BABYLONIA (as implied in Mathematical Thought From Ancient to Modern Times, v. I, pp. 8-10, Morris Kline).