Answer to Question #301814 in Algebra for kavya

Question #301814

1. Find the greatest common divisor of the following polynomials over F, the field of rational numbers: (a) x 3 - 6x 2 + x + 4 and x 5 - 6x + 1. (b) x 2 + 1 and x6 + x 3 + x + 1. 


1
Expert's answer
2022-03-02T12:42:25-0500

(a)

f(x)=x36x2+x+4g(x)=x56x+1g:fx56x+1x36x2+x+4x56x4+x3+4x2x2+6x+356x4x34x26x+16x436x3+6x2+24x35x310x230x+135x3210x2+35x+140200x265x139f(x)=x^3-6x^2+x+4\\ g(x)=x^5-6x+1\\ g:f\\ \begin{matrix} x^5-6x+1 &|x^3-6x^2+x+4 \\ x^5-6x^4+x^3+4x^2 & x^2+6x+35\\ ---------\\ 6x^4-x^3-4x^2-6x+1\\ 6x^4-36x^3+6x^2+24x\\ -----------\\ 35x^3-10x^2-30x+1\\ 35x^3-210x^2+35x+140\\ ----------\\ 200x^2-65x-139 \end{matrix}

r=200x265x139f:rr=200x^2-65x-139\\ f:r

x36x2+x+4200x265x139x1135200x31200x2+200x+800200x365x2139x1135x2+339x+80022700x2+67800x+16000022700x2+73775x+1577655975x+22351195x+447\begin{matrix} x^3-6x^2+x+4 & |200x^2-65x-139 \\ ------- & x-1135\\ 200x^3-1200x^2+200x+800\\ 200x^3-65x^2-139x\\ --------\\ -1135x^2+339x+800\\ ---------\\ -22700x^2+67800x+160000\\ -22700x^2+73775x+157765\\ --------\\ -5975x+2235\\ ------\\ -1195x+447 \end{matrix}

r1=1195x+447r:r1200x265x1391195x+447200x+234523900x2+77675x+16610523900x2+89400x11725x+1661052345x+332212802275x396990952802275x1048215386508800gcd(f,g)=1r_1=-1195x+447\\ r:r_1\\ \begin{matrix} 200x^2-65x-139 &|-1195x+447 \\ -------& 200x+2345\\ -23900x^2+77675x+166105\\ -23900x^2+89400x\\ -------\\ -11725x+166105\\ --------\\ 2345x+33221\\ ------\\ -2802275x-39699095\\ -2802275x-1048215\\ -----\\ -38650880\neq0 \end{matrix}\\ gcd(f,g)=1

(b)

f(x)=x6+x3+x+1g(x)=x2+1f:gx6+x3+x+1x2+1x6+x4x4x2+x+1x4+x3+x+1x4x2x3+x2+x+1x3+xx2+1x2+10gcd(f,g)=x2+1f(x)=x^6+x^3+x+1\\ g(x)=x^2+1\\ f:g\\ \begin{matrix} x^6+x^3+x+1& |x^2+1 \\ x^6+x^4 & x^4-x^2+x+1\\ -----\\ -x^4+x^3+x+1\\ -x^4-x^2\\ -----\\ x^3+x^2+x+1\\ x^3+x\\ -----\\ x^2+1\\ x^2+1\\ -----\\0 \end{matrix}\\ gcd(f,g)=x^2+1


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