ข้อสอบคณิต O-NET - 2551

$$\begin{gathered} \mathrm{จากโจทย์} \mathrm{มาเช็คแต่ละข้อ} \\ \mathrm{จะได้} \\ 1) {\left(x-2\right)}^2 = -1 \\ \mathrm{กำลัง} 2 \mathrm{จะติดลบไม่ได้} \mathrm{ผิด} \\ 2) \left(x^2+2\right)\left(x^2-1\right) = 0 \\ \mathrm{จะได้} \\ = \left(x^2+2\right)\left(x-1\right)\left(x+1\right)=0 \\ \mathrm{ดังนั้น} x=1, -1 \mathrm{ผิด} \end{gathered}$$

$$\begin{gathered} 3) {\left(x-1\right)}^2\left(x^2+2\right) = 0 \\ \mathrm{ดังนั้น} x=1 \mathrm{ผิด} \\ 4) \left(x^2-1\right){\left(x+2\right)}^2 = 0 \\ \mathrm{จะได้} \\ = \left(x-1\right)\left(x+1\right){\left(x+2\right)}^2 = 0 \\ \mathrm{ดังนั้น} x=1, -1, -2 \mathrm{ถูก} \end{gathered}$$