а^(-n) = (1/a)^n.
1) 3^(-4) = (1/3)^4 = 1/81;
2) (-2)^(-6) = (-1/2)^6 = 1/64;
3) (-5)^(-3) = (-1/5)^3 = - 1/125;
4) (-1/8)^(-1) = (-8)^1 = - 8.
