12. The function \(f\) is given by
$$f ( x ) = \mathrm { e } ^ { x } \cos x$$
- Show that \(f ^ { \prime \prime } ( x ) = - 2 \mathrm { e } ^ { x } \sin x\).
- Determine the Maclaurin series for \(f ( x )\) as far as the \(x ^ { 4 }\) term.
- Hence, by differentiating your series, determine the Maclaurin series for \(\mathrm { e } ^ { x } \sin x\) as far as the \(x ^ { 3 }\) term.
- The equation
$$10 \mathrm { e } ^ { x } \sin x - 11 x = 0$$
has a small positive root. Determine its approximate value, giving your answer correct to three decimal places.