ข้อสอบคณิต O-NET - 2554

$$\begin{gathered} \mathrm{จากโจทย์} f\left(x-2\right) = 2x-1 \\ \mathrm{จะได้} f\left(x-2\right) \to f\left(x^2\right) \\ f\left(x-2\right) \to f\left(k^2\right) \to f\left(x^2\right) \end{gathered}$$

$$\begin{gathered} \mathrm{กำหนดให้} x-2 = k^2 \\ x = k^2+2 \\ \mathrm{จะได้} f\left(k^2\right) = 2\left(k^2+2\right)-1 \\ = 2k^2+4-1 \\ = 2k^2+3 \\ \mathrm{ดังนั้น} f\left(x^2\right) = 2k^2+3 \\ \mathrm{ตอบ} \mathrm{ข้อ} 3. \end{gathered}$$