By T W Körner

During this enticing and readable booklet, Dr. Körner describes a number of energetic subject matters that proceed to intrigue expert mathematicians. the themes variety from the layout of anchors and the conflict of the Atlantic to the outbreak of cholera in Victorian Soho. the writer makes use of rather basic phrases and concepts, but explains problems and avoids condescension. when you are a mathematician who desires to clarify to others the way you spend your operating days, then search proposal the following. This e-book will attract everybody attracted to the makes use of of arithmetic

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Extra resources for The pleasures of counting

Sample text

Prove that if x e G then the left coset to which x belongs is {xh: h e H}, and show that this coset is in one-to-one correspondence with H. Deduce Lagrange's theorem^ which states that the number of elements in a subgroup of a finite group G is a factor of the number of elements in G. Show that the same conclusion could be reached by considering * right cosets' instead of left cosets. 105. Let x and y be elements of a given commutative ring. Show how, within the ring, (x2 +y2)2 can be expressed as the sum of two squares.

Expand j-^—TTT~I—T\ m partial fractions. EXERCISES 184-189 47 184. Give the expression for nCr in terms of factorials, where nCr denotes the coefficient of an~rbr in the expansion of (a + b)n by the binomial theorem. Prove that if p is a prime then p divides pCr for 1 ^ r < p — 1. Hence prove that the divisibility of 2 m — 2 by m is a necessary condition for m to be prime, and by consideration of m = 341 = (2 1 0 -l)/3 show that the condition is not sufficient. 185. Prove that if a < b < c and the function / is continuous on the intervals [a, b] and [b> c] then it is continuous on [a, c].

Show that in the field of rational numbers the equations 4x + 3y+ z = 1, 2x+ y + Az = 1, x - 5 s = 1, EXERCISES 174-177 45 have only one solution, but that in the field of integers modulo 7 they have more than one solution. Find all the solutions in the field of integers modulo 7. Give an example of a pair of linear equations which has no solution in the field of rational numbers but which has solutions in the field of integers modulo 3. 174. (a) Prove algebraically that, if zx and z2 are any two complex numbers, |#i + #2| < I^il + W* Give the geometrical interpretation of this when the complex number x + ty is identified with the point {x,y) of the Cartesian plane.