ข้อสอบคณิต O-NET - 2550

$$\begin{gathered} \mathrm{จากโจทย์} \mathrm{จัดรูปสมการก่อน} \\ \mathrm{จะได้} \\ 8^x-8^x·8^1+8^x·8^2 = 228 \\ 8^x-8·8^x+64·8^x = 228 \\ 8^x\left(1-8+64\right) = 228 \\ 8^x\left(57\right) = 228 \\ 8^x = \frac{228}{57} \end{gathered}$$
$$\begin{gathered} 8^x = 4 \\ {\left(2^3\right)}^x = 2^2 \\ 2^{3x} = 2^2 \\ 3x = 2 \\ \mathrm{ดังนั้น}\hspace{0.17em}\hspace{0.17em} x = \frac{2}{3} \end{gathered}$$