Analysis calculus proof kick start question

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SUMMARY

The discussion centers on proving that a function \( f \) defined on \( \mathbb{R} \) and continuous at \( x=0 \) is also continuous at all \( x \in \mathbb{R} \) given the property \( f(x_{1}+x_{2})=f(x_{1})+f(x_{2}) \) for all \( x_{1},x_{2} \in \mathbb{R} \). Key insights include demonstrating that \( f(0) = 0 \) and utilizing the limit definition of continuity. The proof hinges on showing that \( \lim_{h\rightarrow 0} f(a+h) = f(a) \) for any \( a \), leveraging the additive property of \( f \).

PREREQUISITES
  • Understanding of continuity in real analysis
  • Familiarity with limit definitions of functions
  • Knowledge of properties of additive functions
  • Basic calculus concepts
NEXT STEPS
  • Study the proof of the continuity of additive functions
  • Learn about the implications of continuity at a point in real analysis
  • Explore the properties of functions defined on \( \mathbb{R} \)
  • Review limit theorems and their applications in calculus
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Mathematics students, particularly those studying real analysis, and educators looking for insights into function continuity proofs.

gaborfk
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Homework Statement


Prove: If f is defined on \mathbb{R} and continuous at x=0, and if f(x_{1}+x_{2})=f(x_{1})+f(x_{2}) \forall x_{1},x_{2} \in\mathbb{R}, then f is continuous at all x\in\mathbb{R}.


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The Attempt at a Solution



Need a pointer to get started. Cannot wrap my head around it. I understand that I need to prove that the sum of two continuous functions is continuous also.
 
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there is only one function here, f , it has the property that f(x + y) = f(x) + f(y) for all x, y


hint, show f(0) = 0
 
I know that the function is continuous at x=0. So how does showing it is continuous at zero help with showing the function with the property f(x_{1}+x_{2})=f(x_{1})+f(x_{2}) is continuous?

Thank you
 
f is continuous at x= a if and only if
\lim_{x\rightarrow a}f(x)= f(a)[/itex]. <br /> <br /> If h= x- a, then x= a+ h and h goes to 0 as x goes to a: that becomes <br /> \lim_{h\rightarrow 0}f(x+a)= f(a).
 
Hi gaborfk! :smile:

Hint: f(a + epsilon) = f(a) + f(epsilon) :smile:
 

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