- #1
DotKite
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Homework Statement
Let X be the set of continuous functions ## f:\left [ a,b \right ] \rightarrow \mathbb{R} ##.
Let d*(f,g) = ## \int_{a}^{b}\left | f(t) - g(t) \right | dt ## for f,g in X. For each f in X set,
## I(f) = \int_{a}^{b}f(t)dt ##
Prove that the function ## I ##: (X,d*) → (X,d) is continuous
Homework Equations
The definition of d is given as d(## a_{i},b_{i} ##) = max ## \left \{ \left | a_{i} - b_{i} \right | \right \} ##
Here is the definition of continuity I am working with
Let (X,d) and (Y,d') be metric spaces, and let a be in X. A function f : X→Y is said to be continuous at the point a in X if ## \varepsilon > 0 ## and there exists a ## \delta > 0 ## such that
d'(f(x),f(a)) < ## \varepsilon ##
whenever x is in X and
d(x,a) < ## \delta ##
The Attempt at a Solution
Let ## \varepsilon > 0 ##, there exists a ## \delta > 0 ## such that if d*(f,g) < ## \delta ##
then
d(I(f), I(g)) = max {|I(f) - I(g)|} = max ## \left \{ \left | I(f)-I(g) \right | \right \} ## = max ## \left \{ \left | \int_{a}^{b} f(t)dt - \int_{a}^{b}g(t) dt \right | \right \} ## = max ## \left \{ \left | \int_{a}^{b} f(t) - g(t) dt \right | \right \} ##...
So I was thinking that i should let ## \delta = \varepsilon ## and somehow show
max ## \left \{ \left | \int_{a}^{b} f(t) - g(t) dt \right | \right \} ## < ## \delta ##
I could show that by showing max ## \left \{ \left | \int_{a}^{b} f(t) - g(t) dt \right | \right \} ## < ## \int_{a}^{b}\left | f(t)-g(t) \right |dt ## because d(f,g) < ## \delta ##
But I don't think that inequality is true, and this is where I am stuck