Suppose that f: R → R is a function such that f(x+y) = f(x) + f(y) for every x, y E R. Prove that f has a limit at 0 if and only if f has a limit at every c ER. Hints: The "if" part is trivial, so it's the "only if" part that requires work. Hints to do this: first show that f(1/n) = f(1)/n for any natural number n. Now show that if f has a limit at 0, then the limit itself must be 0. Complete the proof from there.

College Algebra
1st Edition
ISBN:9781938168383
Author:Jay Abramson
Publisher:Jay Abramson
Chapter3: Functions
Section3.3: Rates Of Change And Behavior Of Graphs
Problem 2SE: If a functionfis increasing on (a,b) and decreasing on (b,c) , then what can be said about the local...
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Suppose that f: R → R is a function such that f(x+y) = f(x) + f(y)
for every x, y E R. Prove that f has a limit at 0 if and only if f has a
limit at every c ER.
Hints: The "if" part is trivial, so it's the "only if" part that requires
work. Hints to do this: first show that f(1/n) = f(1)/n for any natural
number n. Now show that if f has a limit at 0, then the limit itself
must be 0. Complete the proof from there.
Transcribed Image Text:Suppose that f: R → R is a function such that f(x+y) = f(x) + f(y) for every x, y E R. Prove that f has a limit at 0 if and only if f has a limit at every c ER. Hints: The "if" part is trivial, so it's the "only if" part that requires work. Hints to do this: first show that f(1/n) = f(1)/n for any natural number n. Now show that if f has a limit at 0, then the limit itself must be 0. Complete the proof from there.
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