$$\sqrt {1+x}\le 1+\dfrac {x}{2}\ \ ,\ \ \ \sqrt {1+2x}\le 1+x$$ $$\sqrt {(2x+1)(1-3x)}=\sqrt {1-(x+6x^2)}\le 1-\dfrac {x (6+x)}{2}$$ $$\sqrt {(1-3x)(x+1)}=\sqrt {1-(2x+3x^2)}\le 1-\dfrac {x (2+3x)}{2}$$ $$3 \le (x+1)\left ( 1+\dfrac {x}{2}\right)(1+x)+(2x+1)\left (1-\dfrac {x (6+x)}{2}\right)+(1-3x)\left (1-\dfrac {x (2+3x)}{2}\right)$$ $$3\le 3-\dfrac {x^2 (1+2x)}{2} \Rightarrow x =0$$ отвечен 21 Янв '22 15:31 Sergic Primazon |