If se c^2 + ta n^2 = 712 , then se c^4 - ta n^4 = ?

Answer: Option A

$$\begin{array}{rl}& \left(\text{se}{\text{c}}^4\theta -\text{ta}{\text{n}}^4\theta \right)\\ & \Rightarrow \left(\text{se}{\text{c}}^2\theta -\text{ta}{\text{n}}^2\theta \right)\left(\text{se}{\text{c}}^2\theta +\text{ta}{\text{n}}^2\theta \right)\\ & \Rightarrow 1\times \left(\text{se}{\text{c}}^2\theta +\text{ta}{\text{n}}^2\theta \right)[1+\text{ta}{\text{n}}^2\theta =\text{se}{\text{c}}^2\theta ]\\ & \Rightarrow 1\times \frac{7}{12}\\ & \Rightarrow \frac{7}{12}\end{array}$$