b: A=2B
=>\(\dfrac{\sqrt{x}}{\sqrt{x}+3}=\dfrac{2\left(8\sqrt{x}-3\right)}{14}=\dfrac{8\sqrt{x}-3}{7}\)
=>\(\left(8\sqrt{x}-3\right)\left(\sqrt{x}+3\right)=7\sqrt{x}\)
=>\(8x+24\sqrt{x}-3\sqrt{x}-9-7\sqrt{x}=0\)
=>\(8x+14\sqrt{x}-9=0\)
=>\(\left(4\sqrt{x}+9\right)\left(2\sqrt{x}-1\right)=0\)
=>\(2\sqrt{x}-1=0\)
=>\(\sqrt{x}=\dfrac{1}{2}\)
=>\(x=\dfrac{1}{4}\left(nhận\right)\)