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Understanding Limits: Using Notation

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  • 0:06 Defining Limits
  • 2:02 Finding Limits
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Lesson Transcript
Instructor: Jeff Calareso

Jeff teaches high school English, math and other subjects. He has a master's degree in writing and literature.

Join me on a road trip as we define the mathematical notation of limits. As time goes by and I traverse hills and highways, the limit of my speed changes. Learn how to write these limits in this lesson.

Defining Limits

Roadtrip graph showing speed as a function of time
Limits of roadtrip

Limits describe what happens as you approach some number. But how do we write this mathematically? Let's go back to a road trip of mine. I'm going to plot my speed as a function of time. I'm going to start out and drive along the city streets. Then I'm going to get on the highway and cruise along at 60 mph or so. I'll go over a hill where my car slows down. When I go down the hill, I start going too fast. Then I'm going to get pulled over for speeding. I'm going to say that when I get pulled over for speeding, that's about at a time roughly 40 minutes in. So I'm going to say that my time, which I'll call t, is 40. How do we write the limit as I approach one of these times? So what is the limit? The limit is the value that a function approaches as your variable approaches some number. In this case, the variable of interest, the variable I care about, is time. Our function is speed.

What is the limit that my speed takes as I approach 10 minutes? Well, if I'm on a highway, I'm probably going about 60 mph. Mathematically, I'd write the limit as time goes to 10 of my function's speed, which is a function of time, is 60. Similarly, I could say that the limit as time approaches 20 of my speed is about 45 mph. We know that when I go uphill, I can only get up to about 45 mph. Lastly, I can say that the limit as time approaches 30 of my speed is maybe 70 mph. This is what I was going when the cop found me.

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