8 It is given that \(\mathrm { y } = \operatorname { coshu }\), where \(u > 0\), and $$\sqrt { \cosh ^ { 2 } u - 1 } \left( \frac { d ^ { 2 } u } { d x ^ { 2 } } + \frac { d u } { d x } \right) + \cosh u \left( \frac { d u } { d x } \right) ^ { 2 } - 2 \cosh u = 4 e ^ { - x }$$

1. Show that $$\frac { d ^ { 2 } y } { d x ^ { 2 } } + \frac { d y } { d x } - 2 y = 4 e ^ { - x }$$
2. Find \(u\) in terms of \(x\), given that, when \(x = 0 , u = \ln 3\) and \(\frac { d u } { d x } = 3\).
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