ข้อสอบคณิต O-NET - 2556

$$\begin{gathered} \mathrm{จากสูตร} {\left(น-ล\right)}^2 = {น}^2-2\mathrm{นล}+{ล}^2 \\ \mathrm{จากโจทย์} \frac{1}{{\left(1-\sqrt{3}\right)}^2} = \frac{1}{1-2\sqrt{3}+3} \\ = \frac{1}{4-2\sqrt{3}} \\ = \frac{1}{2\left(2-\sqrt{3}\right)}\times \frac{\left(2+\sqrt{3}\right)}{\left(2+\sqrt{3}\right)} \end{gathered}$$

$$\begin{gathered} = \frac{2+\sqrt{3}}{2\left(4-3\right)} \\ = \frac{2+\sqrt{3}}{2} \\ = \frac{2+1.732}{2} \\ = \frac{3.732}{2} \\ = 1.866 \\ \mathrm{ดังน้ัน} \mathrm{ตอบข้อ} 4 \end{gathered}$$