\[\lim_{k \to \infty}\sum_{k}^{\infty } \left [ \frac{3}{7}\times \left ( \frac{12}{49} \right )^{k}\times \left (\frac{4}{7} \right )^{2} + \left ( \frac{12}{49} \right ) ^{k}\times \left (\frac{4}{7} \right )^{2} \right] \]
\[ = \frac{48+112}{259} \]
\[ =\frac{160}{259} \]
承年獸老師的說法，答案應該這樣吧。
