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

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

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4<br />

Remov<strong>in</strong>g the brackets <strong>and</strong> collect<strong>in</strong>g the terms <strong>of</strong> the same degree <strong>in</strong><br />

we obta<strong>in</strong> the equation<br />

The coefficient <strong>of</strong> <strong>in</strong> this equation is equal to Therefore if we<br />

put after substitut<strong>in</strong>g we transform the equation<br />

<strong>in</strong>to:<br />

where <strong>and</strong> are some polynomials <strong>in</strong> <strong>and</strong><br />

Let be a root <strong>of</strong> Eq. (6). Represent<strong>in</strong>g it <strong>in</strong> the form<br />

(where <strong>and</strong> are temporarily unknown) we obta<strong>in</strong><br />

<strong>and</strong><br />

We check whether it is possible to impose that <strong>and</strong> satisfy<br />

In this case we obta<strong>in</strong> two equations for <strong>and</strong><br />

By Viète’s <strong>theorem</strong>, for any such <strong>and</strong> (which may be complex)<br />

<strong>in</strong>deed exist, <strong>and</strong> they are the roots <strong>of</strong> the equation<br />

If we take such (still unknown) <strong>and</strong> then Eq. (7) is transformed <strong>in</strong>to<br />

Rais<strong>in</strong>g either terms <strong>of</strong> the equation to the third power, <strong>and</strong><br />

compar<strong>in</strong>g the obta<strong>in</strong>ed equation with Eq. (8), we have

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