By Paul J. Nahin

ISBN-10: 0691127980

ISBN-13: 9780691127989

Today complicated numbers have such common functional use--from electric engineering to aeronautics--that few humans could anticipate the tale in the back of their derivation to be packed with event and enigma. In *An Imaginary Tale*, Paul Nahin tells the 2000-year-old heritage of 1 of mathematics' such a lot elusive numbers, the sq. root of minus one, sometimes called *i*. He recreates the baffling mathematical difficulties that conjured it up, and the colourful characters who attempted to unravel them.

In 1878, while brothers stole a mathematical papyrus from the traditional Egyptian burial web site within the Valley of Kings, they led students to the earliest identified prevalence of the sq. root of a adverse quantity. The papyrus provided a selected numerical instance of ways to calculate the quantity of a truncated sq. pyramid, which implied the necessity for *i*. within the first century, the mathematician-engineer Heron of Alexandria encountered *I *in a separate venture, yet fudged the mathematics; medieval mathematicians stumbled upon the concept that whereas grappling with the that means of adverse numbers, yet brushed off their sq. roots as nonsense. by the point of Descartes, a theoretical use for those elusive sq. roots--now known as "imaginary numbers"--was suspected, yet efforts to unravel them resulted in excessive, sour debates. The infamous *i* eventually received reputation and was once placed to exploit in advanced research and theoretical physics in Napoleonic times.

Addressing readers with either a basic and scholarly curiosity in arithmetic, Nahin weaves into this narrative exciting ancient proof and mathematical discussions, together with the appliance of advanced numbers and capabilities to special difficulties, comparable to Kepler's legislation of planetary movement and ac electric circuits. This publication should be learn as an attractive heritage, virtually a biography, of 1 of the main evasive and pervasive "numbers" in all of mathematics.

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**Extra resources for An Imaginary Tale: The Story of ?-1**

**Sample text**

Consider the following statement, easily shown to be correct with a little arithmetic on the back of an envelope: (22 ϩ 32) (42 ϩ 52) ϭ 533 ϭ 72 ϩ 222 ϭ 232 ϩ 22. And this one, which is only just a bit more trouble to verify: (172 ϩ 192) (132 ϩ 152) ϭ 256,100 ϭ 642 ϩ 5022 ϭ 82 ϩ 5062. What is going on here? These are two examples of a general theorem that says the product of two sums of two squares of integers is always expressible, in two different ways, as the sum of two squares of integers. That is, given integers a, b, c, and d, we can always find two pairs of positive integers u and v such that (a2 ϩ b2) (c2 ϩ d2) ϭ u2 ϩ v2.

Since xˆ Ϫ k 0, we can divide through both sides of this equation to obtain a quadratic in xˆ , ϭ xˆ 2 Ϫ 2pˆx ϩ p2 ϩ q2. 4. A cubic equation with one real root. 29 CHAPTER ONE In fact, since T is a point of tangency, there must be exactly one value of xˆ . That is, xˆ 2 Ϫ 2pˆx ϩ p2 ϩ q2 Ϫ ϭ 0 must have two equal, or double, roots. Now, in general, xˆ = 2 p ± 4 p 2 − 4( p 2 + q 2 − λ ) , 2 and to have double roots the radical must be zero. That is, 4p2 Ϫ 4(p2 ϩ q2 Ϫ ) ϭ 0 or, ϭ q2. That is, the tangent line AT has slope q2 ϭ TM/AM.

27 At first glance this sixth-degree equation may look like a huge step backward, but in fact it isn’t. The equation is, indeed, of the sixth degree, but it is also quadratic in u3. So, using the solution formula for quadratics, well-known since Babylonian times, we have u3 = q q 2 p3 ± + . 2 4 27 or, using just the positive root,2 9 CHAPTER ONE 3 u= q q 2 p3 . + + 2 4 27 Now, since v3 ϭ q Ϫ u3, then 3 v= q q 2 p3 . − + 2 4 27 Thus, a solution to the depressed cubic x3 ϩ px ϭ q is the fearsome-looking expression 3 x= 3 q q 2 p3 + + + 2 4 27 q q 2 p3 .

### An Imaginary Tale: The Story of ?-1 by Paul J. Nahin

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