ข้อสอบคณิต O-NET - 2562

$$\begin{gathered} \mathrm{จากโจทย์} \\ f\left(-11\right) \mathrm{ใช้สูตร} \left(\mathrm{เพราะ} -11 < 10\right) \\ \mathrm{จะได้} f\left(-11\right) = -\frac{-11}{4}+8 = \frac{11}{4}+8 \\ f\left(20\right) \mathrm{ใช้สูตรบน} \left(\mathrm{เพราะ} 20 \ge 10\right) \\ \mathrm{จะได้} f\left(20\right) = \frac{20}{4}-12 = -7 \end{gathered}$$

$$\begin{gathered} \mathrm{ดังนั้น} f\left(-11\right)+f\left(20\right) \\ = \frac{11}{4}+8+\left(-7\right) \\ = 2.75+1 \\ = 3.75 \end{gathered}$$