lim [(1 - 6х/7)^(-7/6x)]^(-6x^2/ (7*(3x-3))
<=> lim e^(-6x^2/ (7*(3x-3))
<=> lim e^(-2x^2/ (7*(x-1))
<=> e^lim(-2x^2/ (7*(x-1))

вот так