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No function satisfying the condition

Source: KJMO 2017 p7

July 26, 2019
algebraKJMO

Problem Statement

Prove that there is no function f:R0Rf:\mathbb{R}_{\ge0}\rightarrow\mathbb{R} satisfying:
f(x+y2)f(x)+yf(x+y^2)\ge f(x)+y for all two nonnegative real numbers x,yx,y.