Có: [tex]B=\frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+...+\frac{1}{\sqrt{99}+\sqrt{100}}=\frac{\sqrt{2}-\sqrt{1}}{2-1}+\frac{\sqrt{3}-\sqrt{2}}{3-2}+...+\frac{\sqrt{100}-\sqrt{99}}{100-99}=-\sqrt{1}+\sqrt{100}=9[/tex]
[tex]\Rightarrow x^{3}+3Bx^{2}+27Bx+9B^{2}=0\Leftrightarrow x^{3}+3.9x^{2}+27.9.x+9.9^{2}=0\Leftrightarrow (x+9)^{3}=0[/tex] nên pt đã cho có 1 nghiệm x=-9