calculus – Is it true that $A=int(A)$ or $A=int(A) cup fr(A)$ and true that $A^C=ext(A)$ or $A=ext(A) cup fr(A)$?

I’m trying to understang some topology of $mathbb{R}^n$ space.

I want to know if it’s true that $A=int(A)$ or $A=int(A) cup fr(A)$ and true that $A^C=ext(A)$ or $A=ext(A) cup fr(A)$

Further more, if $A=int(A)cup fr(A)$, then $A^C=ext(A)$ and if $A=int(A)$, then $A^C=ext(A)cup fr(A)$