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

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Solutions 177<br />

b) In order for to vary<br />

cont<strong>in</strong>uously one may choose The variation <strong>of</strong> the argument<br />

along the curve will thus be Hence the<br />

variation <strong>of</strong> the argument along curve (cf., 280) is equal to<br />

<strong>and</strong> the argument <strong>of</strong> is equal to<br />

Answer.<br />

c) The variation <strong>of</strong> the argument along the given curve<br />

is: The variation <strong>of</strong> the argument along curve<br />

is equal to The argument <strong>of</strong> is equal to<br />

Answer.<br />

282. Let let be the cont<strong>in</strong>uous image <strong>of</strong> the given curve<br />

with We have to def<strong>in</strong>e We may take<br />

a) the variation <strong>of</strong> is equal to Therefore the variation <strong>of</strong><br />

is equal to (cf., 280), <strong>and</strong><br />

Answer.<br />

b) The variation <strong>of</strong> is equal to<br />

The variation <strong>of</strong> is equal to <strong>and</strong><br />

Answer.<br />

c) the given curve is a circle <strong>of</strong> unit radius, whose centre is moved to<br />

the po<strong>in</strong>t (cf., 246(a)). This curve does not turn at all around the<br />

po<strong>in</strong>t therefore the variation <strong>of</strong> vanishes. It follows that<br />

the variation <strong>of</strong> is also equal to zero.<br />

Answer.<br />

283. Let be the cont<strong>in</strong>uous image <strong>of</strong> the curve C under the<br />

mapp<strong>in</strong>g S<strong>in</strong>ce either or<br />

In order to have it is necessary <strong>and</strong> sufficient<br />

that be equal to where is any <strong>in</strong>teger. To obta<strong>in</strong> this<br />

the variation <strong>of</strong> must be equal to (cf., 280), i.e., the curve C<br />

must turn times around the po<strong>in</strong>t<br />

284. Let <strong>and</strong> be the cont<strong>in</strong>uous images <strong>of</strong> the curves <strong>and</strong><br />

under the mapp<strong>in</strong>g If the curves <strong>and</strong> start from the<br />

same po<strong>in</strong>t (Figure 66) then the curve is a cont<strong>in</strong>uous image<br />

<strong>of</strong> the curve The ends <strong>of</strong> the curve (po<strong>in</strong>ts A <strong>and</strong> B) will<br />

co<strong>in</strong>cide if <strong>and</strong> only if the curve turns around the po<strong>in</strong>t an<br />

even number <strong>of</strong> times (cf., 283).

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