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Question

Question :

One of the factors of x5+x+1 is

(1) 2x2 - x - 1

(2) x3 - x2 + 1

(3) x2 - 2x2 + 1

(4) x3 + x2 + 1

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Solution

x^5+x+1
= x^5 - x^4 + x^4 - x^3 + x^ 3 - x^2 +x^2+x+1
=x^4(x-1) + x^3(x-1) + x^2 (x - 1)+ x^ 2+ x +1
=(x-1)(x^4+x^3+x^2)+(x^2+x+1)
=(x-1)(x^2)(x^2+x+1)+(x^2+x+1)
=(x^2+x+1)(1+(x-1)*x^2)
=(x^2+x+1)(x^3-x^2+1)
So
x^5+x+1=(x^3-x^2+1)(x^2+x+1)

therefore (x^3-x^2+1) is a factore

so option (2) is the right answer

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