Suppose that the function $f:[0,1]\rightarrow \mathbb{R}$ is continuous and that $f\left(x\right)>2$ if $0\leq x<1$. Is it necessarily true that $f\left(1\right)>2$?
My attempt:
Yes, using the sequence definition of continuous.
Since $f$ is continuous at $x=1$, so we can take $x_n\rightarrow 1$ as $n\rightarrow \infty$, then $f\left(x_n\right) \rightarrow f\left(1\right)$ as $n\rightarrow \infty$.
Furthermore, $f\left(x_n\right)>2$ $\forall$ $x_n$ where $0\leq x_n < 1$.
$\implies f\left(1\right)>2$.
Does this make sense?
Best Answer
You need to be careful with the distinction between $\geq$ and $\gt$. Specifically, just because a sequence has values that are $\gt 2$, it doesn't mean that the limit is $\gt2$, just that it's $\geq2$.
In your case, $f(x)=3-x$ fulfills the criteria, but $f(1) =2$.