We have indeterminateness of type
0/0,
i.e. limit for the numerator is
x→0+limtan(mx)=0and limit for the denominator is
x→0+limsin(nx)=0Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
x→0+lim(sin(nx)tan(mx))=
x→0+lim(∂x∂sin(nx)∂x∂tan(mx))=
x→0+lim(ncos(nx)m(tan2(mx)+1))=
x→0+lim(nm)=
x→0+lim(nm)=
nmIt can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 1 time(s)