The decimal representation of some real numbers is not unique. For example, prove mathematically that $0.\dot{9} \equiv 0.9999\cdots \equiv 1$.
Let $x = 0.9999\cdots$. Then, $$ 10x = 9.9999\cdots = 9 + x \; \Rightarrow \; 9x = 9\; \Rightarrow \; x = 1. $$