MathDB
Two polynomials, a division

Source: Iran 3rd round 2011-Number Theory exam-P3

September 19, 2012
algebrapolynomialRing Theorymodular arithmeticnumber theory proposednumber theory

Problem Statement

P(x)P(x) and Q(x)Q(x) are two polynomials with integer coefficients such that P(x)Q(x)2+1P(x)|Q(x)^2+1.
a) Prove that there exists polynomials A(x)A(x) and B(x)B(x) with rational coefficients and a rational number cc such that P(x)=c(A(x)2+B(x)2)P(x)=c(A(x)^2+B(x)^2).
b) If P(x)P(x) is a monic polynomial with integer coefficients, Prove that there exists two polynomials A(x)A(x) and B(x)B(x) with integer coefficients such that P(x)P(x) can be written in the form of A(x)2+B(x)2A(x)^2+B(x)^2.
Proposed by Mohammad Gharakhani