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Abel's theorem in problems and solutions - School of Mathematics

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188 Problems <strong>of</strong> Chapter 2<br />

CD.<br />

S<strong>in</strong>ce the function has a f<strong>in</strong>ite number <strong>of</strong> branch po<strong>in</strong>ts then<br />

one can choose the curves AB <strong>and</strong> CD sufficiently short <strong>and</strong> the curves<br />

CA <strong>and</strong> BD sufficiently close to the cut, <strong>in</strong> such a way that <strong>in</strong> the region<br />

bounded by the curve CABDC there are no branch po<strong>in</strong>ts <strong>of</strong> the function<br />

In this case one can evidently transform the curve CABD <strong>in</strong>to the<br />

curve CD without pass<strong>in</strong>g through any branch po<strong>in</strong>t. S<strong>in</strong>ce the function<br />

possesses the monodromy property, the function at the po<strong>in</strong>t<br />

D is uniquely def<strong>in</strong>ed by cont<strong>in</strong>uity along the curves CD <strong>and</strong> CABD.<br />

Start<strong>in</strong>g from the branch <strong>and</strong> cover<strong>in</strong>g the curve CABD, mov<strong>in</strong>g first<br />

on the branch, one passes later to the branch, mov<strong>in</strong>g f<strong>in</strong>ally on<br />

it. In this way, along the curve CABD <strong>and</strong> therefore also along the curve<br />

CD, one moves from the branch to the branch, exactly as along<br />

the curve AB.<br />

FIGURE 89<br />

311. a) H<strong>in</strong>t. Answer.<br />

(Here is the positive value <strong>of</strong> the square root)<br />

b) ±1/2; c)<br />

0; d) e) 0.<br />

312. H<strong>in</strong>t. It suffices to prove that the functions <strong>and</strong><br />

possess the properties stated by the problem, <strong>and</strong> that if the functions<br />

<strong>and</strong> possess these properties then the functions<br />

(where is an <strong>in</strong>teger) also possess<br />

these properties.<br />

Solution. 1) If then The curve sought is<br />

the curve with the parametric equation where is the<br />

parametric equation <strong>of</strong> the curve C.<br />

2) If then <strong>and</strong> the required curve is the curve with<br />

the equation (degenerated to a po<strong>in</strong>t).<br />

3) Suppose that <strong>and</strong> that the statement <strong>of</strong> the<br />

problem is true for the functions <strong>and</strong> By the def<strong>in</strong>ition <strong>of</strong> the

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