# A History of Geometrical Methods by Julian Lowell Coolidge

By Julian Lowell Coolidge

Full, authoritative historical past of the options for facing geometric equations covers improvement of projective geometry from historic to trendy instances, explaining the unique works, commenting at the correctness and directness of proofs, and displaying the relationships among arithmetic and different highbrow advancements. 1940 edition.

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Let B 1 = B t1 CiB1 П B, B2 = B2 D B 2 ПВ, B n = B 1 U B2 . The sets B1 and B2 do not intersect. It is an immediate consequence of the definition of the function о for open sets that G ( B V ) + G ( B 2 ) = G ( B ff). On the other hand, by the choice of the sets Bi, B2 and B 9, G ( BV) — G (At) < e, G (PV) — о (A2) < 8, g (B) — g (Al и A2) < e, which implies Ia (Ai) + a (A2) — a (A 1 и A2) | < 3 e . , the function о satisfies the first condition. We now verify the validity of the second condition.

In evaluating J 2 , we divide the integration over the e-neighborhood of the circle x (£) into an integration in the direction perpendicular to the circle x (£) and an integration in the direction of x (£). , by 2 я . Therefore, up to terms of order e2, J2 = 2яе2. Finally we consider the integral h = J íttL M ü . У (gil) 2 — Xa FUNK’S PROBLEM 57 Just as for the integral J i , we will distinguish two cases, depending on the relative position of the points £ and tj, namely, Case I : Ш 2 > I — b2> and Case 2 : (r]£)2 < I — X2.

Then the distance function p (X, y) in the domain G, defined by the formula P (x >y) = k p i ( x 9 y) + \x p2( X, y ) , K p ^ 0. obviously satisfies the axioms for a metric space and, therefore, specifies a metric in the domain G. We wish to see that the metric P(*> У) is again a Desarguesian metric. To show this, let g be an arbitrary line and x be an arbitrary point of g. , such that the length of S equals the distance between its endpoints. Since the metric is Desarguesian, there exists an interval S 1 on the line g, containing the point x in its interior, which is a segment in the metric P 1.