4. The coefficient of \(x ^ { 2 }\) in the binomial expansion of \(( 1 + k x ) ^ { 7 }\), where \(k\) is a positive constant, is 525.
- Find the value of \(k\).
Using this value of \(k\),
- show that the coefficient of \(x ^ { 3 }\) in the expansion is 4375,
- find the first three terms in the expansion in ascending powers of \(x\) of
$$( 2 - x ) ( 1 + k x ) ^ { 7 }$$