Rút gọn B=(\frac{1}{\sqrt{x}+2}-\frac{1}{\sqrt{x}+5}):\frac{5}{\sqrt{x}+7} (x\geq 0)

TXĐ: $x∈R$, $x≥0$

$\Bigg(\dfrac{1}{\sqrt[]{x}+2}-\dfrac{1}{\sqrt[]{x}+5}\Bigg):\dfrac{5}{\sqrt[]{x}+7}$

$=\dfrac{\sqrt[]{x}+5-\sqrt[]{x}-2}{(\sqrt[]{x}+2)(\sqrt[]{x}+5)}.\dfrac{\sqrt[]{x}+7}{5}$

$=\dfrac{3(\sqrt[]{x}+7)}{5(\sqrt[]{x}+2)(\sqrt[]{x}+5)}$