We have indeterminateness of type
0/0,
i.e. limit for the numerator is
x→0+lim(sin(x)−tan(x))=0and limit for the denominator is
x→0+limx3=0Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
x→0+lim(x3sin(x)−tan(x))=
x→0+lim(dxdx3dxd(sin(x)−tan(x)))=
x→0+lim(3x2cos(x)−tan2(x)−1)=
x→0+lim(dxd3x2dxd(cos(x)−tan2(x)−1))=
x→0+lim(6x−sin(x)−2tan3(x)−2tan(x))=
x→0+lim(dxd6xdxd(−sin(x)−2tan3(x)−2tan(x)))=
x→0+lim(−6cos(x)−tan4(x)−34tan2(x)−31)=
x→0+lim(−6cos(x)−tan4(x)−34tan2(x)−31)=
−21It can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 3 time(s)