Are my postulates true regarding circles?

1. Nov 8, 2012

student34

If we know the exact radius of a circle, then we can't have an exact circumference, and if we know the exact circumference, then we can't know the exact radius.

If these postulates are true, then I realize that this idea is not original but probably known since B.C.

2. Nov 8, 2012

Vorde

Exact isn't the right word to use. If I have a circle with diameter 1, I know that the circumference is exactly $\pi$, I just can't represent $\pi$ by a finite decimal sequence.

However you are right in your idea, a circle cannot simultaneously have a rational circumference and a rational radius.