Let f(x) be a differentiable function at x = a with f ^ ' (a) = 2...

${f}^{'}\left(a\right) = 2, f\left(a\right) = 4$

$\lim_{x \to a}\dfrac{xf\left(a\right) - af\left(x\right)}{x - a}$

$⇒ \lim_{x \to a}\dfrac{f\left(a\right) - a{f}^{'}\left(x\right)}{1}$ (L'Hospitals rule)

$= f\left(a\right) - a{f}^{'}\left(a\right)$

$= 4 - 2a$