2. The equation \(x ^ { 2 } + 5 k x + 2 k = 0\), where \(k\) is a constant, has real roots.
- Prove that \(k ( 25 k - 8 ) \geq 0\).
- Hence find the set of possible values of \(k\).
- Write down the values of \(k\) for which the equation \(x ^ { 2 } + 5 k x + 2 k = 0\) has equal roots.