Detail solution
Let's take the limit
x→−∞lim(3x)Let's divide numerator and denominator by x:
x→−∞lim(3x) =
x→−∞lim31x11Do Replacement
u=x1then
x→−∞lim31x11=u→0+lim(u3)=
03=−∞The final answer:
x→−∞lim(3x)=−∞
Lopital's rule
There is no sense to apply Lopital's rule to this function since there is no indeterminateness of 0/0 or oo/oo type
Other limits x→0, -oo, +oo, 1