Consider the function if a €Q -22 if r ¢ Q. f(x) = Prove that f'(0) = 0. Hint: The fact stated in Question 10 of Problem Set 2 is usef

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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can the fact in solution of question number 10 use to solve this question? any expert please help if you know how to use it

Consider the function
if a € Q
f(r) =
if æ ¢ Q.
Prove that f'(0) = 0.
Hint: The fact stated in Question 10 of Problem Set 2 is useful.
Transcribed Image Text:Consider the function if a € Q f(r) = if æ ¢ Q. Prove that f'(0) = 0. Hint: The fact stated in Question 10 of Problem Set 2 is useful.
10) First, we prove the forward direction. Assume lim f(r) = 0. We need to show that
エ→a
lim |f(r)| = 0. Fix e > 0. We need to find some 8 > 0 such that whenever 0 < |r - a| < 8,
we have ||f(r)| - 0| < e. Since lim f(x) = 0, we can choose d > 0 such that whenever
0< |x – a| < 8, we have |f(x) – 0| < e. With this d, it follows that whenever 0 < |r – a| < 8,
we have ||f(x)| – 0| = |f(x)| < e as required.
Conversely, assume lim |f(x)| = 0. We need to show that lim f(x) = 0. Fix e > 0. We
エ→a
エ→4
need to find some o > 0 such that whenever 0 < |a - al < 8, we have |f(r) – 0| < e. Since
lim |f(x)| = 0, we can choose ô > 0 such that whenever () < |r-a| < 8, we have || f(x)|- 0| < e.
With this d, it follows that whenever 0 < |r – a| < 8, we have |f (x) – 0 = ||f(x)|| < e as
required.
Transcribed Image Text:10) First, we prove the forward direction. Assume lim f(r) = 0. We need to show that エ→a lim |f(r)| = 0. Fix e > 0. We need to find some 8 > 0 such that whenever 0 < |r - a| < 8, we have ||f(r)| - 0| < e. Since lim f(x) = 0, we can choose d > 0 such that whenever 0< |x – a| < 8, we have |f(x) – 0| < e. With this d, it follows that whenever 0 < |r – a| < 8, we have ||f(x)| – 0| = |f(x)| < e as required. Conversely, assume lim |f(x)| = 0. We need to show that lim f(x) = 0. Fix e > 0. We エ→a エ→4 need to find some o > 0 such that whenever 0 < |a - al < 8, we have |f(r) – 0| < e. Since lim |f(x)| = 0, we can choose ô > 0 such that whenever () < |r-a| < 8, we have || f(x)|- 0| < e. With this d, it follows that whenever 0 < |r – a| < 8, we have |f (x) – 0 = ||f(x)|| < e as required.
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