Absolute Values and Continuous Functions

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SUMMARY

The discussion centers on the mathematical concept that while a continuous function f guarantees the continuity of its absolute value |f|, the reverse is not true. A specific example provided is the piecewise function f(x) = -1 for x < 0 and f(x) = 1 for x ≥ 0, where |f(x)| is continuous at all points, yet f(x) itself is not continuous. Another example includes defining f as -1 on rational numbers and 1 on irrational numbers, further illustrating this principle.

PREREQUISITES
  • Understanding of continuous functions in real analysis
  • Familiarity with piecewise functions
  • Knowledge of absolute value properties
  • Basic concepts of rational and irrational numbers
NEXT STEPS
  • Study the properties of continuous functions in real analysis
  • Explore examples of discontinuous functions and their absolute values
  • Investigate the implications of continuity in different mathematical contexts
  • Learn about the topology of real numbers and its relation to continuity
USEFUL FOR

Students of mathematics, particularly those studying real analysis, educators teaching continuity concepts, and anyone interested in the properties of functions and their absolute values.

Rosey24
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Homework Statement



We recently proved that if a function, f, is continuous, it's absolute value |f| is also continuous. I know, intuitively, that the reverse is not true, but I'm unable to come up with an example showing that, |f| is continuous, b f is not. Any examples or suggestions would be appreciated. Thanks!

Homework Equations



The Attempt at a Solution

 
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What about f(x) = -1 if x &lt; 0 and 1 if x \ge 0?
Then |f(x)| = 1 for all x - about as continuous as you get them, but f is not. In fact, you could even do something pathetic like make f equal -1 on all rationals and 1 on all irrational numbers :)
 

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