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Real and Complex Analysis (Rudin)

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4 REAL AND COMPLEX ANALYSIS<br />

We shall encounter the integral of (1 + X 2 )-1 over the real line. To evaluate<br />

it, put tp(t) = sin tlcos t in (-nI2, nI2). By (6), tp' = 1 + tp2. Hence tp is a monotonically<br />

increasing mapping of ( -nI2, n12) onto ( - 00, (0), <strong>and</strong> we obtain<br />

foo ~ = fft/2 tp'(t) :t = f"/2 dt = n.<br />

-00 1 + X -ft/2 1 + tp (t) -ft/2

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