دانلود کتاب Modern geometry with applications

Chapter 1 on Euclidean geometry displays the author’s poor taste as well as his profound misconception of what it means to prove something. We learn on page 19 that the area of a triangle is (1/2)(base)(height). The only justification for this is that it is “often” clear by cutting and pasting. Fine. We don’t have to prove every little thing. But then there follows a “proposition 1.8.1” in which Jennings supposedly “proves”, by using this formula, that moving the tip of a triangle along a line parallel to the base doesn’t change its area. Jennings is also very fond of isometries and use them to “prove” SAS congruence. Since the discussion of isometries is purely descriptive, with no claims to axiomatic status, this essentially amounts to saying that “the triangles are congruent because I say so”, no matter how much it is padded with fancy language (let T be the isometry such that this-and-that, etc.). Although this proof is questionable, at least here Jennings is in the company of Euclid (I.4). But Jennings quickly proves himself unworthy of such dignified company by proving SSS using the cosine theorem, which is certainly not Euclid’s proof (I.8). Some other parts of the book are less disastrous, especially when Jennings borrows lots of material from Courant & Robbins and Hilbert & Cohn-Vossen. Still, Jennings almost manages to destroy even these beautiful things through thoroughly tasteless exposition; the proofs typically consist of elaborate justifications of trivial details by mountains of useless symbolism while the key ideas are not addressed at all (“It is important to note that [something completely trivial]: this is because blah, blah, blah, define L(z_4*), blah, blah, blah. It is clear that [important step], so we’re done.”). It is also ridiculous to claim that “projective geometry blossomed during the eighteenth [century]” (p. 115).