This file is part of a distribution of the Calculus Applets website (http://www.calculusapplets.com) (v1.1) which has been reformatted for the needs of this OpenCourseware course.

A function *f *can have a specific value for an input. For example,
if *f *(*x*) = 0.5*x* then *f *(5) = 2.5. For continuous
functions like this one, as *x* approaches 5, the output value of *f *approaches 2.5. For some other functions, however, we can extend this
concept to cases where the function is not continuous or even has no value.
Informally, we say that if *f *(*x*) approaches *L* as *x* approaches *c*, then *L* is called the limit. We write
this mathematically as .

Try the following:

- The first graph show the line used in the example above. Is the limit
*L*= 0.5 when*c*= 1 ? In other words, does*f*(*x*) approach 0.5 as*x*approaches 1? Move the*x*slider so that*x*gets closer and closer to 1. For this example, the limit does equal 0.5. In fact,*f*(1) = 0.5 in this case, but as we will see, this does not need to be the case.

- Select the second example. This is just like the first case, except
that one point has moved. Is the limit still
*L*= 0.5 when*c*= 1 ? In other words, does*f*(*x*) approach 0.5 as*x*approaches 1? Move the*x*slider so that*x*gets closer and closer to 1. For this example, the limit still equals 0.5. As*x*gets closer and closer to*c*= 1,*f*(*x*) gets closer and closer to*L*= 0.5. The limit is**not**1.5, even though that is the value of the function at*x*= 1. Instead, the limit is the output value that is*approached*as the input value*approaches*1. For functions that are continuous around the point of interest, as in the first example, it is easy to find the limit; you just evaluate the function at the specific input, because the output value it approaches is the same as the function's output value at that point. But for cases like this second example, there still is a limit but it happens to be different than the value of the function.

- Select the third example. This is like the previous two cases, but
there is now a point missing. Is the limit still
*L*= 0.5 when*c*= 1 ? In other words, does*f*(*x*) approach 0.5 as*x*approaches 1? Move the*x*slider so that*x*gets closer and closer to 1. For this example, the limit still equals 0.5. As*x*approaches*c*= 1,*f*(*x*) approaches*L*= 0.5. Even though the function has no value at all at*x*= 1, there is still a valid limit there, as the function does approach a specific output value.

- Select the fourth example. This is a more complex function, but this
example is similar to the previous one with a missing point. What is the
limit when
*c*= 0 ? In other words, what value does*f*(*x*) approach as*x*approaches 0? Move the*x*slider so that*x*gets closer and closer to 0. For this example, the limit equals 1. As*x*gets closer and closer to*c*= 0,*f*(*x*) gets closer and closer to*L*= 1. Even though the function has no value at all at*x*= 0, there is still a valid limit there, as the function does approach a specific value. Mathematically, we would write .

Limits are part of the foundation of the theory of calculus. They can also make the informal definition of continuity more formal.

For more information on rights and downloading, refer to http://www.calculusapplets.com/download.html.

© Copyright 2001 David J. Eck

© Copyright 2007 Thomas S. Downey

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

You must cause any files that you modify to carry prominent notices stating that you changed the files and the date of any change, and modified files must be put into a Java package different from edu.hws.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Citation: tdowney. (2009, August 06). Informal Limits. Retrieved August 22, 2014, from Notre Dame OpenCourseWare Web site: http://ocw.nd.edu/mathematics/elements-of-calculus-i/calculus-applets-website/Informal%20Limits.html.

Copyright 2012,
Thomas S. Downey.
This work is licensed under a
Creative Commons Attribution 3.0 License.