Suppose that the function f:[0,1]→R is continuous and that f(x)>2 if 0≤x<1. Is it necessarily true that f(1)>2?
My attempt:
Yes, using the sequence definition of continuous.
Since f is continuous at x=1, so we can take xn→1 as n→∞, then f(xn)→f(1) as n→∞.
Furthermore, f(xn)>2 ∀ xn where 0≤xn<1.
⟹f(1)>2.
Does this make sense?
Answer
You need to be careful with the distinction between ≥ and >. Specifically, just because a sequence has values that are >2, it doesn't mean that the limit is >2, just that it's ≥2.
In your case, f(x)=3−x fulfills the criteria, but f(1)=2.
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