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Continuity & Properties of functions

  • #1

Homework Statement



Let f:R->R be a continuous function where limit as x goes to positive/negative infinity is negative infinity. Prove that f has a maximum value on R.

Homework Equations


None


The Attempt at a Solution


I tried to use the definition of infinite limits but I'm not sure how to do this explicitly.
 

Answers and Replies

  • #2
HallsofIvy
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Let X be a real number. Since [itex]\lim_{x\rightarrow \infty}= -\infty[/itex], there exist x1[/sup] such that if x> x1, f(x)< X. Since [itex]\lim_{x\rightarrow -\infty}= -\infty[/itex], there exist x2 such that if x< x2, f(x)< X. Now look at the values of f(x) on the closed and bounded interval [x1, x2].
 

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