# 1.4 Continuity, One-Sided Limits, and Intermediate Value Theorem

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1.4 Continuity, One-Sided Limits, and Intermediate Value Theorem
Grand Canyon, Arizona Greg Kelly, Hanford High School, Richland, Washington Photo by Vickie Kelly, 2002

This function has discontinuities at x=1 and x=2.
Most of the techniques of calculus require that functions be continuous. A function is continuous if you can draw it in one motion without picking up your pencil. A function is continuous at a point if the limit is the same as the value of the function. 1 2 3 4 This function has discontinuities at x=1 and x=2. It is continuous at x=0 and x=4, because the one-sided limits match the value of the function

Removable Discontinuities:
(You can fill the hole.) Essential Discontinuities: infinite oscillating jump

Removing a discontinuity:
has a discontinuity at Write an extended function that is continuous at Note: There is another discontinuity at that can not be removed.

Removing a discontinuity:
Note: There is another discontinuity at that can not be removed.

Continuous functions can be added, subtracted, multiplied, divided and multiplied by a constant, and the new function remains continuous. Also: Composites of continuous functions are continuous. examples:

THIS IS THE DEFINITION OF CONTINUITY
A function f is continuous at a point x = c if f (c) is defined 1. 2. 3. THIS IS THE DEFINITION OF CONTINUITY

Example f (x) = x – 1 at x = 2. f (2) = a. 1 b. The limit exist! c.
Therefore the function is continuous at x = 2.

Example f (x) = (x2 – 9)/(x + 3) at x = -3 a. - 6 b. c. f (-3) = 0/0
Is undefined! b. - 6 -3 The limit exists! c. -6 Therefore the function is not continuous at x = -3. You can use table on your calculator to verify this.

Continuity Properties
If two functions are continuous on the same interval, then their sum, difference, product, and quotient are continuous on the same interval except for values of x that make the denominator 0. Every polynomial function is continuous. Every rational function is continuous except where the denominator is zero.

Continuity Summary. Graph on your calculator with a standard window. Functions have three types of discontinuity. Consider - 1. Discontinuity at vertical asymptote. 2. Discontinuity at hole. 3. We have discontinuity with some functions that have a gap.

Intermediate Value Theorem
If a function is continuous between a and b, then it takes on every value between and Because the function is continuous, it must take on every y value between and

Intermediate Value Theorem: Intuition
Traveling on France’s TGV trains, you reach speed of 280 mi/hr. How do you know at some point of train ride you were traveling 100 mi/hr? To go from 0 to 280, must have passed through 100 mi/hr since speed of train changed continuously

Intermediate Value Theorem
Suppose that f is continuous on the closed interval [a,b]. If L is any real number between f(a) and f(b) then there must be at least one number c on the open interval (a,b) such that f(c) = L.

Limitations of IVT If d(0) = 100 and d(10) = 35, where t is measured in seconds. d is a continuous function, the IVT tells you that at some point between t=0 and t =10, the decibel level reached every value between 35 and 100. It does NOT say anything about: When or how many times (other than at least once) a particular decibel was attained. Whether or not decibel levels bigger than 100 or less than 35 were reached.

The Difference Between VROOOOOOOOM and VROOOOOOOM.
These graphs of PC's noise illustrate that very different behaviors are consistent with the hypothesis that d(t) is continuous and that its values at t=0 and t=10 are 100 and 35 respectively.

Example 1: Sketch a graph to decide if the cosecant function, f(x) = csc (x) is continuous over the domain [-π, π].

Example 2 Consider the equation sin x = x – 2 . Use the intermediate Value Theorem to explain why there must be a solution between π/2 and π.

Example 3 Consider the function , Calculate f(6), f(-5.5), f(0)
Can you conclude that there must be a zero between f(6) and f(-5.5)?

Is any real number exactly one less than its cube?
Example 5: Is any real number exactly one less than its cube? (Note that this doesn’t ask what the number is, only if it exists.) Since f is a continuous function, by the intermediate value theorem it must take on every value between -1 and 5. Therefore there must be at least one solution between 1 and 2. Use your calculator to find an approximate solution. F2 1: solve

Graphing calculators can sometimes make non-continuous functions appear continuous.
CATALOG F floor( This example was graphed on the classic TI-89. You can not change the resolution on the Titanium Edition. Note resolution. The calculator “connects the dots” which covers up the discontinuities.

Graphing calculators can make non-continuous functions appear continuous.
CATALOG F floor( If we change the plot style to “dot” and the resolution to 1, then we get a graph that is closer to the correct floor graph. The open and closed circles do not show, but we can see the discontinuities. GRAPH p