6 The equation
$$9 x ^ { 3 } - 9 x ^ { 2 } + x - 2 = 0$$
has roots \(\alpha , \beta , \gamma\).
- Use the substitution \(y = 3 x - 1\) to show that \(3 \alpha - 1,3 \beta - 1,3 \gamma - 1\) are the roots of the equation
$$y ^ { 3 } - 2 y - 7 = 0$$
The sum \(( 3 \alpha - 1 ) ^ { n } + ( 3 \beta - 1 ) ^ { n } + ( 3 \gamma - 1 ) ^ { n }\) is denoted by \(S _ { n }\).
- Find the value of \(S _ { 3 }\).
- Find the value of \(S _ { - 2 }\).