If $${\text{se}}{{\text{c}}^2}\theta + {\text{ta}}{{\text{n}}^2}\theta = \frac{7}{{12}}{\text{,}}$$     then $${\text{se}}{{\text{c}}^4}\theta $$  - $${\text{ta}}{{\text{n}}^4}\theta $$   = ?

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