$$\frac{(x+1)^{2}}{6} + \frac{(x-1)^{2}}{12} - \frac{x^{2}-1}{4} = 1$$
Домножим обе части уравнения на 12:
$$2(x+1)^{2} + (x-1)^{2} - 3(x^{2}-1) = 12$$
$$2(x^{2}+2x+1) + x^{2}-2x+1 - 3x^{2}+3 = 12$$
$$2x^{2}+4x+2 + x^{2}-2x+1 - 3x^{2}+3 = 12$$
$$2x^{2}+x^{2}-3x^{2}+4x-2x+2+1+3-12 = 0$$
$$2x-6 = 0$$
$$2x = 6$$
$$x = 3$$
Ответ: 3.