Problem

Source: Malaysian SST 2024 P4

Tags: algebra



Fix a real polynomial $P$ with degree at least $1$, and a real number $c$. Prove that there exist a real number $k$ such that for all reals $a$ and $b$, $$P(a)+P(b)=c \quad \Rightarrow \quad |a+b|<k$$ Proposed by Wong Jer Ren