a/ $2x^3+6x^2=x^2+3x\\↔2x^2(x+3)-x(x+3)=0\\↔(2x^2-x)(x+3)=0\\↔x(2x-1)(x+3)=0\\↔x=0\quad or\quad 2x-1=0\quad or\quad x+3=0\\↔x=0\quad or\quad x=\dfrac{1}{2}\quad or\quad x=-3$
Vậy pt có tập nghiệm $S=\bigg\{0;\dfrac{1}{2};-3\bigg\}$
b/ $\dfrac{1}{x}+2=\bigg(\dfrac{1}{x}+2\bigg)(x^2-3)\\↔\bigg(\dfrac{1}{x}+2\bigg)-\bigg(\dfrac{1}{x}+2\bigg)(x^2-3)=0\\↔\bigg(\dfrac{1}{x}+2\bigg)(4-x^2)=0\\↔\dfrac{1}{x}+2=0\quad or\quad 4-x^2=0\\↔\dfrac{1}{x}=-2\quad or\quad x^2=4\\↔x=-\dfrac{1}{2}\quad or\quad x=±2$
Vậy pt có tập nghiệm $S=\bigg\{-\dfrac{1}{2};2;-2\bigg\}$
