If a/b = 256 , then the value of a^2 - b^2a^2 + b^2 is?

Answer: Option B

$$\begin{array}{rl}& \frac{a}{b}=\frac{25}{6}\\ & \frac{a^2}{b^2}=\frac{{25}^2}{6^2}\\ & \Rightarrow \frac{a^2-b^2}{a^2+b^2}\\ & \Rightarrow \frac{{25}^2-6^2}{{25}^2+6^2}\\ & \Rightarrow \frac{625-36}{625+36}\\ & \Rightarrow \frac{589}{661}\end{array}$$