Proving the Algebraicity of u-1 over Field K in Extension Field F

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SUMMARY

The discussion centers on proving that if u is algebraic over field K, then u-1 is also algebraic over K in the extension field F. A participant suggests avoiding contradiction and instead finding a polynomial that u^(-1) satisfies. They provide an example where if u satisfies the polynomial x^2 + 2x + 3, then u^(-1) satisfies the polynomial 1 + 2x + 3x^2. This establishes a method for demonstrating the algebraicity of u-1.

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Homework Statement


K is a field, F is an extension field of K.
If u is algebraic over K, u an element of F, show u-1 is algebraic over K

I'm trying to find a contradiction when I assume u-1 is transcendental, but I am not getting very far... anything to steer me in the right direction.
 
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Don't try and do it by contradiction. If u is algebraic then it's a root of a polynomial over K. Try and find a polynomial that u^(-1) satisfies. Here's an example. If u satisfies x^2+2x+3, I'm pretty sure u^(-1) will satisfy 1+2x+3x^2. Why?
 

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