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##\textbf{Definition 1:}## Let ##R## be an UFD. A nonzero polynomial in ##R[x]## is said to be ##\textbf{primitive}## if the only constants that divides it are the units in ##R##.
##\textbf{Definition 2:}## Let ##R## be an UFD. Hence highest common factors of finite subsets of ##R## exists, by collecting common factors of the unique factorization of the elements into products of irreducibles.A polynomial ##f(x)\in R[x]## is called ##\textbf{primitive}## if the highest common factors of the non-zero coefficients of ##f(x)## is equal to ##1##. This implies that if ##u\in R## and ##u|f(x)## then ##u## is a unit in ##R.##
##\textbf{Exercise:}## Prove that a polynomial is ##\textbf{primitive}## if and only if ##1_R## is a greatest common divisor of its coefficients. This property is often taken as the definition of primitive.
##\textit{Hint:}## Since ##c_1c_2\cdots c_mf(x)=g(x),## each ##c_i## divides ##g(x).## Therefore, ##c_i## is a unit in ##R##, because ##g(x)## is primitive.
For ##\textbf{Exercise}##, it says the statement in the Exercise can be taken to be the definition of primitive polynomial instead of ##\textbf{Definition 1}##. But according to ##\textbf{Definition 2}##, it seems that the statement of ##\textbf{Exercise}## implies ##\textbf{Definition 1}##. Regardless if it is an implication or an equivalent statements. How does one go about proving either?
Another thing is, how does gcd related to units in a commutative ring, ED, PID or UFD?
Thank you in advance.
##\textbf{Definition 2:}## Let ##R## be an UFD. Hence highest common factors of finite subsets of ##R## exists, by collecting common factors of the unique factorization of the elements into products of irreducibles.A polynomial ##f(x)\in R[x]## is called ##\textbf{primitive}## if the highest common factors of the non-zero coefficients of ##f(x)## is equal to ##1##. This implies that if ##u\in R## and ##u|f(x)## then ##u## is a unit in ##R.##
##\textbf{Exercise:}## Prove that a polynomial is ##\textbf{primitive}## if and only if ##1_R## is a greatest common divisor of its coefficients. This property is often taken as the definition of primitive.
##\textit{Hint:}## Since ##c_1c_2\cdots c_mf(x)=g(x),## each ##c_i## divides ##g(x).## Therefore, ##c_i## is a unit in ##R##, because ##g(x)## is primitive.
For ##\textbf{Exercise}##, it says the statement in the Exercise can be taken to be the definition of primitive polynomial instead of ##\textbf{Definition 1}##. But according to ##\textbf{Definition 2}##, it seems that the statement of ##\textbf{Exercise}## implies ##\textbf{Definition 1}##. Regardless if it is an implication or an equivalent statements. How does one go about proving either?
Another thing is, how does gcd related to units in a commutative ring, ED, PID or UFD?
Thank you in advance.
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