Question Number 140468 by mathdanisur last updated on 08/May/21
$${a};{b};{c}\in\mathbb{R}\:;\:\forall\mid{x}\mid\leqslant\mathrm{1} \\ $$$$\mid{ax}^{\mathrm{4}} +{bx}^{\mathrm{2}} +{c}\mid\sqrt{\mathrm{1}−{x}^{\mathrm{2}} }\leqslant\mathrm{1}\:;\:{proof}\:\mid{a}\mid\leqslant\mathrm{16} \\ $$
Commented by mathdanisur last updated on 11/May/21
$${Sir},\:{mr}.{W}\:{my}\:{dear}\:{friend}\:{please}… \\ $$