05.01.2013 Views

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

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

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

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

The complex numbers 71<br />

2.8 Images <strong>of</strong> curves: the basic <strong>theorem</strong><br />

<strong>of</strong> the algebra <strong>of</strong> complex numbers<br />

Consider two planes <strong>of</strong> complex numbers: the plane <strong>and</strong> the plane,<br />

<strong>and</strong> a function which puts <strong>in</strong>to correspondence with every<br />

value a value uniquely def<strong>in</strong>ed. If on the plane there is a cont<strong>in</strong>uous<br />

curve C hav<strong>in</strong>g equation then by the function every po<strong>in</strong>t<br />

<strong>of</strong> this curve is sent to a po<strong>in</strong>t <strong>of</strong> the plane. Hence if the function<br />

is cont<strong>in</strong>uous we also obta<strong>in</strong> on the plane a cont<strong>in</strong>uous curve, hav<strong>in</strong>g<br />

equation We shall denote this curve by<br />

261. What is the curve if <strong>and</strong> the curve C is<br />

a) a quarter <strong>of</strong> a circle:<br />

b) a semi-circle:<br />

c) a circle:<br />

262. Let the variation <strong>of</strong> the argument along a curve C be equal to<br />

What is the variation <strong>of</strong> the argument along the curve if: a)<br />

b) c) where is a non-zero arbitrary<br />

<strong>in</strong>teger?<br />

263. Suppose that the curve C turns times around the po<strong>in</strong>t<br />

How many times does the curve turn around the po<strong>in</strong>t if<br />

264. Suppose that a curve C turns around the po<strong>in</strong>ts<br />

respectively times. How many times does<br />

the curve turn around the po<strong>in</strong>t if: a) b)<br />

c) d)<br />

Consider the equation<br />

where all the are arbitrary complex numbers, <strong>and</strong><br />

Our first aim is to show that this equation has at least one complex root.<br />

If then the equation possesses the root In the sequel,<br />

therefore, we will assume that<br />

Let us denote by A the maximum amongst the numbers<br />

S<strong>in</strong>ce A > 0. Choose two real numbers <strong>and</strong> with<br />

such conditions: let be sufficiently small to satisfy the <strong>in</strong>equalities:<br />

<strong>and</strong> let be sufficiently large to satisfy the<br />

<strong>in</strong>equalities: <strong>and</strong>

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!