If f : \(\mathbb{R}\) → \(\mathbb{R}\) is a differentiable function at a ∈ \(\mathbb{R}\) such that f'(a) = af(a), then \(\mathop {Lt}\limits_{x \to a} \frac{{xf\left( a \right) - af\left( x \right)}}{{x - a}} =\)
1
(1 - a2) f (a)
2
\(\frac{f(a)}{a}\)
3
af (a)
4
\(\frac{f(a)}{1-a^2}\)