In: Advanced Math
a) Let f(x) be continuous at any point c.
Then there exists a sequence,
converging to
, such that the sequence
converges to
.
Then by definition, for
,
such that
for
for
and
((By sequential criteria for continuity.))
Now by triangle inequality we know that :
for
Hence for a sequence
converging to
, the sequence
converges to
.
Therefore, by sequential criteria for continuity,
is continuous.
b) Consider the function
It can easily be proven that this function is not continuous at any point.
But
at every point. And is hence, continuous at each and every
point.
Therefore, the converse may not be true. That is, if
is continuous at a point
, that does not mean that
will be continuous at
.