Find the product of 2x^3+3x^2+1 and 2x^2+4 in z_5[x]/<x^3+1>

Yulia

Yulia

Answered question

2021-09-16

Find the product of 2x3+3x2+1 and 2x2+4 in z5[x]/<x3+1>

Answer & Explanation

Talisha

Talisha

Skilled2021-09-17Added 93 answers

Group of integers modulo 5
Z5={0,1,2,3,4}
Now,
Z5[x] denotes the ring of polynomials with coefficients from Z5 and <x3+1> denotes the principal ideal generated by (x3+1) that is
<x3+1>={f(x)(x3+1)|f(x)Z5[x]|}
Z5[x]/<x3+1>={g(x)+<x3+1>g(x)Z5[x]}
={ax2+bx+c+<x3+1>a,b,cZ5}
We know that
x3+1+<x3+10+<x3+1>
So, x3+1 is equivalent 0
Equivalently, x3=1
Now 2x3+3x2+1=2(1)+3x2+1+<x3+1>
=3x21+<x3+1>
=3x2+4+<x3+1>Z5[x]/<x3+1>
since 14 in Z5
2x2+4=2x2+4+<x3+1>Z5[x]/<x3+1>
Product of given two polynomials
(2x3+3x2+1)(2x2+4)=(3x2+4+<x3+1>)(2x2+4+<x3+1>)
=6x4+20x2+16+<x3+1>
Since x3=1 implies x4=x
So we have

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