Given that \(f(x)=6x^3+5x^2-17x-6\),

- find the remainder when \(f(x)\) is divided by \(x-2\),
- find the remainder when \(f(x)\) is divided by \(x+2\),
- factorise \(f(x)\) completely.

Given that the expression \(ax^3-x^2+bx+18\) is exactly divisible by \(x^2+x-6\), find the value of \(a\) and \(b\).