Why is x^2 + 1 an Irreducible Polynomial?

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In summary, x^2 + 1 is irreducible because it cannot be factored over the real numbers, but it can be factored over the complex numbers. On the other hand, x^2 + x + 1 has no real solutions because the discriminant is negative.
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mathdad
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Why is x^2 + 1 irreducible?
 
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  • #2
RTCNTC said:
Why is x^2 + 1 irreducible?

What do you think? If you factor this expression, what do you get? Moreover, what could be said about those factors in relation to the real numbers?
 
  • #3
Complex numbers?
 
  • #4
Indeed!

In this case we could say that the expression is irreducible over the reals, but reducible over the complex numbers. But I might let someone else chime into give a more formal approach. :)
 
  • #5
Cool.
 
  • #6
What about x^2 + x + 1?
 
  • #7
RTCNTC said:
What about x^2 + x + 1?

What does the discriminant tell you about the roots of this quadratic polynomial?
 
  • #8
b^2 - 4ac

1^2 - 4(1)(1)

1 - 4

-3

b^2 - 4ac < 0

This means no real solutions.
 

FAQ: Why is x^2 + 1 an Irreducible Polynomial?

What is an irreducible polynomial?

An irreducible polynomial is a polynomial that cannot be factored into polynomials of lower degree with coefficients from the same field. In other words, it cannot be broken down into simpler terms.

How do you determine if a polynomial is irreducible?

There are several methods for determining if a polynomial is irreducible, depending on the degree of the polynomial. One method is to use the rational roots theorem to check if there are any rational roots. If there are no rational roots, then the polynomial is irreducible. Another method is to use the Eisenstein criterion, which involves checking if the coefficients of the polynomial satisfy certain conditions. If they do, then the polynomial is irreducible.

What is the significance of irreducible polynomials?

Irreducible polynomials have several important applications in mathematics, particularly in algebra and number theory. They are used to construct field extensions, which are essential for various mathematical computations. They also play a role in finding roots of polynomials and solving polynomial equations.

Can a polynomial be both reducible and irreducible?

No, a polynomial cannot be both reducible and irreducible. A polynomial is either one or the other. A polynomial may be reducible in one field, but irreducible in another.

Are irreducible polynomials used in real-world applications?

Yes, irreducible polynomials have practical applications in fields such as coding theory, cryptography, and signal processing. They are also used in various engineering and science applications, such as in error-correcting codes and in the design of communication systems.

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