## Do Irreducibles Induce Algebraic Extensions?

Given $$K$$ a field, and $$f\in K[x]$$ an irreducible (monic) polynomial. Does it follow that the field $$K[x]/\left<f\right>$$ is an algebraic extension of $$K$$?

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 Recognitions: Homework Help Science Advisor i think so. in general, if M is a maximal ideal in a commutative ring R, then R/M is a field. If R contains a subfield k, then R/M is an extension of k. So in your case the ring K[X] contains the subfield K, and since K[X] is a Euclidean ring, hence also a p.i.d., an irreducible polynomial f generates a maximal ideal, so K[X]/(f) is a field extension of K. Moreover the degree (vector dimension) of the extension equals the degree of f, hence is finite, and every finite extension is definitely algebraic. so YES! I had to think through all the details since I am old and losing my memory. hope this helps.
 Recognitions: Gold Member Science Advisor Staff Emeritus Isn't the answer obvious from the definition of "algebraic extension"? The interesting part is that it's a field and not just a ring. (Hrm. I suppose there are equivalent definitions, and some would be less obvious than others. Which are you using?)