Domain of a any cubic function
is defined to be always
.
The derivative with respect to x of your cubic function is,
![(d)/(dx)f(x)=f'(x)](https://img.qammunity.org/2022/formulas/mathematics/college/gidxejdistfk856q1w5l5879clw32luvx3.png)
to find the derivative of a polynomial function, simply take a derivative of each factor and sum them up,
by the rule
where
![m\in\mathbb{R}](https://img.qammunity.org/2022/formulas/mathematics/college/mku7wzjsesou7f64f16icrhyq565u9klcm.png)
![(d)/(dx)-6x=-6](https://img.qammunity.org/2022/formulas/mathematics/college/d10tfrkin2ey6ffs75m8u8geqbk501wved.png)
![(d)/(dx)3=0](https://img.qammunity.org/2022/formulas/mathematics/college/a3et1fb6f2uaxq97ywxql3r735rt88iuk8.png)
So the derivative is,
![f'(x)=3x^2-6](https://img.qammunity.org/2022/formulas/mathematics/college/wkxt4ech2hresh0redyt81h9xnj0l1u6ei.png)
both derivative and the original function have equal domain.
Hope this helps :)