Tomamos como el límite
$$\lim_{x \to 1^+}\left(\frac{- 5 x + \left(12 - 6 x^{2}\right)}{- 4 x + \left(x^{2} - 1\right)}\right)$$
cambiamos
$$\lim_{x \to 1^+}\left(\frac{- 5 x + \left(12 - 6 x^{2}\right)}{- 4 x + \left(x^{2} - 1\right)}\right)$$
=
$$\lim_{x \to 1^+}\left(\frac{- 6 x^{2} - 5 x + 12}{x^{2} - 4 x - 1}\right)$$
=
$$\lim_{x \to 1^+}\left(\frac{6 x^{2} + 5 x - 12}{- x^{2} + 4 x + 1}\right) = $$
$$\frac{-12 + 5 + 6 \cdot 1^{2}}{- 1^{2} + 1 + 4} = $$
= -1/4
Entonces la respuesta definitiva es:
$$\lim_{x \to 1^+}\left(\frac{- 5 x + \left(12 - 6 x^{2}\right)}{- 4 x + \left(x^{2} - 1\right)}\right) = - \frac{1}{4}$$