Let $f$ be a function defined on the interval $(a, c]$. Then $f$ is continuous from the left at the number $c$ if $ \lim _{x \rightarrow c^{-}} f(x)=f(c) $ Let $f$ be a function defined on the interval $[c, b)$. Then $f$ is continuous from the right at the number $c$ if $ \lim _{x \rightarrow c^{+}} f(x)=f(c) $