[tex](1)<=>(\frac{1}{1+\sqrt{x}}-\frac{1}{\sqrt{x+3}})+(\frac{1}{1+\sqrt{x}}-\frac{1}{\sqrt{3x-1}})=0\Leftrightarrow \frac{(x+3)-(1+\sqrt{x}^{2})}{(1+\sqrt{x})\sqrt{x+3}[(\sqrt{x+3}+(1+\sqrt{x})]}+\frac{(3x+1)-(1+\sqrt{x})^{2}}{\sqrt{3x+1}(1+\sqrt{x})[\sqrt{3x+1}+(1+\sqrt{x})]=0\Leftrightarrow 2(1-\sqrt{x})(\frac{1}{\sqrt{....}}\sqrt})[/tex] =0
Chứng minh BT trong ngoặc dương dễ dàng bạn nhé!