$3\sqrt{10}=\sqrt{3^2.10}=\sqrt{90}$

$4\sqrt{5}=\sqrt{4^2.5}=\sqrt{80}$

Vì $90>80\iff \sqrt{90}>\sqrt{80}$ Hay $3\sqrt{10}>4\sqrt{5}$

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$3\sqrt{2}=\sqrt{3^2.2}=\sqrt{18}$

$2\sqrt{3}=\sqrt{2^2.3}=\sqrt{12}$

$5=\sqrt{25}>\sqrt{24}=2\sqrt{6}$

$4=\sqrt{16}<\sqrt{19}$

$4\sqrt{3}=\sqrt{48}<\sqrt{49}=7$

$\iff$ 36x² - 12x - 36x² + 27x = 30

$\iff$ 15x = 30

$\iff$ x = 30 : 15 = 2

$3x\left(12x-4\right)-9x\left(4x-3\right)=30$

$\iff 36x^2-12x-36x^2+27x=30$

$\iff 15x=30$

$\iff x=2$

Vậy $S=\left\{2\right\}$

$\left(12x-5\right)\left(4x-1\right)+\left(3x-7\right)\left(1-16x\right)=81$

$\iff 48x^2-12x-20x+5+3x-48x^2-7+112x=81$

$\iff 83x-2=81$

$\iff 83x=83$

$\iff x=1$

Vậy $S=\left\{1\right\}$

$\iff 48x^2-12x-20x+5+3x-48x^2-7+112x=81$

$\iff 83x=83$

=>x=1

(2+x)(x2−2x+4)−(3+x2)⋅x=14⇔x3+8−x3−3x=14⇔(x3−x3)−3x+8=14⇔−3x+8=14⇔−3x=6⇔x=−2

$(2+x)(x^2-2x+4)-(3+x^2)x=14$

$\iff x^3+8-3x-x^3=14$

$\iff -3x=6$

$\iff x=-2$

Vậy $S=\{-2\}$

$\iff x^3+8-x^3-3x=14$

=>-3x=6

hay x=-2