# Real Analysis/Limits and Continuity Exercises/Hints

From Wikibooks, open books for an open world

←Exponential Function | Real AnalysisExercises |
Differentiation→ |

### Exercises[edit]

*These problems are on the difficult or, to put it differently if not mildly, non-standard type. Try to work the problems without the hints because most times, you might have a different approach or way of thinking about a problem. Use the hints only if you are truly stuck! Without further ado, here are the problems:*

- Prove that the function, f(x) = 1/x is not uniformly continuous on the interval (0,∞).
- Prove that a convex function is continuous (Recall that a function is a
*convex function*if for all and all with , ) - Prove that every continuous function
*f*which maps [0,1] into itself has at least one fixed point, that is such that - Prove that the space of continuous functions on an interval has the cardinality of
- Let be a monotone function, i.e. . Prove that has countably many points of discontinuity.
- Let be a differentiable function, and suppose there is some positive constant such that for all . (a) Prove that is Lipschitz continuous on (Hint: Use the mean value theorem). (b) Show that every function which is Lipschitz continuous is also uniformly continuous (and therefore the function you are working with is uniformly continuous).

**Hints**/Answers[edit]

- No Hint.
- You may want to prove first that the region above a convex function is convex (i.e. any straight line joining two points in the region, lies wholly in the region) and then using this fact argue by way of contradiction to show that convex functions are indeed continuous (i.e. no jump or removable discontinuity)
- Consider the function . Using the Intermediate Value Property, show that such that .
- First show that the set of all infinite sequences of real numbers has the same cardinality as and next show that every continuous function is determined by it's values on
- No hint.
- (a) Use mean value theorem, once we cover it. (b) Let .