Can someone point me to an article or textbook where I can learn more about the reduction technique used in the third answer titled Rational Root Theorem Solution to the question asked in Factorization of quartic polynomial.? The key point that interests me in that answer was how the potential quartic factor $x^2-px-q$ is written as $x^2 = p x + q$ and how this last expression is used as a reduction rule.
I am asking if anyone knows if the reduction approach used in this particular answer is developed or discussed in detail in some article or textbook?
Thank you.
