ข้อสอบคณิต O-NET - 2561

$$\begin{gathered} \mathrm{จากโจทย์} \\ \sqrt{\frac{x}{8}}+\frac{11}{20} = \sqrt[3]{\frac{64}{125}} \\ \mathrm{จะได้} \sqrt{\frac{x}{8}}+\frac{11}{20} = \sqrt[3]{\frac{4^3}{5^3}} \\ \sqrt{\frac{x}{8}}+\frac{11}{20} = \frac{4}{5} \\ \sqrt{\frac{x}{8}} = \frac{4}{5}-\frac{11}{20} \end{gathered}$$

$$\begin{gathered} \sqrt{\frac{x}{8}} = \frac{16-11}{20} \\ \sqrt{\frac{x}{8}} = \frac{5}{20} = \frac{1}{4} \\ \frac{x}{8} = \frac{1}{16} \\ x = \frac{1}{2} \\ \mathrm{ดังน้ัน} \mathrm{อยู่ในช่วง} [0, 2) \to \mathrm{ตอบข้อ} 1 \end{gathered}$$