Find the first three terms, in ascending powers of \(x\), in the expansion of \(( 1 + a x ) ^ { 6 }\).
Given that the coefficient of \(x ^ { 2 }\) in the expansion of \(( 1 - 3 x ) ( 1 + a x ) ^ { 6 }\) is - 3 , find the possible values of the constant \(a\).