Investigate Limit of Piecewise Function

In summary, the conversation is about interpreting the graph of a piecewise function to determine the limit of the function as x approaches a certain value, c. The instructions were initially incorrect, but the correct problem was eventually posted. The conversation also touches on the concept of continuity and how it relates to determining the limit. Ultimately, it is concluded that the limit does not exist at c due to a hole in the graph.
  • #1
nycmathguy
Homework Statement
Graphs & Limits
Relevant Equations
Piecewise Function
My apologies. I posted the correct problem with the wrong set of instructions. It it a typo at my end. Here is the correct set of instructions for 28:

Use the graph to investigate limit of f(x) as x→c. If the limit does not exist, explain why.

For (a), the limit is 1.

For (b), the limit DOES NOT EXIST.

You say?

For (c), the LHL does not = RHL.

I conclude the limit DOES NOT EXIST.
 

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  • #2
nycmathguy said:
For (a), the limit is 1.
How is that possible? 1 is not in the domain of the function as x -> 2, just when you GET TO 2.

I think the problem here is that you are using the concept of "limit" when it should not be applied. The VALUE of the function is 2 when x=2. Period.
 
  • #3
phinds said:
How is that possible? 1 is not in the domain of the function as x -> 2, just when you GET TO 2.

I think the problem here is that you are using the concept of "limit" when it should not be applied. The VALUE of the function is 2 when x=2. Period.
Yes, but ##\displaystyle{\lim_{x \nearrow c}f(x)=1}##. ##f(2)## cannot be determined.
 
  • #4
nycmathguy said:
Homework Statement:: Graphs & Limits
Relevant Equations:: Piecewise Function

Use the graph to investigate the following:

(a) lim of f(x) as x→2 from the left side.

(b) lim of f(x) as x→2 from the right side.

(c) lim of f(x) as x→2.

For (a), the limit is 1.

For (b), the limit is 2.

For (c), the LHL does not = RHL.
You should say ##x \to c## not ##x \to 2##. The last one means, that the ##f(x)## is not continuous at ##x=c##. ##f(c)=2## but ##\lim_{x\to c} f(x)## has no determined value, because both possible paths lead to a different value.
nycmathguy said:
I conclude the limit for y = f(x) DNE.
?
 
  • #5
fresh_42 said:
Yes, but ##\displaystyle{\lim_{x \nearrow c}f(x)=1}##. ##f(2)## cannot be determined.
We are interpreting the graph in opposite ways. I interpret the black to dot to be a value and the white dot to be empty and you are interpreting it the opposite way. Is there are standard for this?

EDIT: your follow-on post clarifies this
 
  • #6
phinds said:
We are interpreting the graph in opposite ways. I interpret the black to dot to be a value and the white dot to be empty and you are interpreting it the opposite way. Is there are standard for this?
Me, too. But you supposed ##c=2## which hasn't been said.
 
  • #7
fresh_42 said:
Me, too. But you supposed ##c=2## which hasn't been said.
see my EDIT
 
  • #8
phinds said:
How is that possible? 1 is not in the domain of the function as x -> 2, just when you GET TO 2.

I think the problem here is that you are using the concept of "limit" when it should not be applied. The VALUE of the function is 2 when x=2. Period.

See my editing work.
 
  • #9
fresh_42 said:
Yes, but ##\displaystyle{\lim_{x \nearrow c}f(x)=1}##. ##f(2)## cannot be determined.

See my editing work. If f(2) cannot be determined due to the hole at (1, 2), the LHL DOES NOT = RHL. I conclude the limit does not exist.

You say?
 
  • #10
nycmathguy said:
See my editing work. If f(2) cannot be determined due to the hole at (1, 2), the LHL DOES NOT = RHL. I conclude the limit does not exist.

You say?
The (two-sided) limit cannot not detemined, ##f(c)=2## can, as can the one-sided limits.
 
  • #11
fresh_42 said:
Me, too. But you supposed ##c=2## which hasn't been said.

My apologies. I posted the correct problem with the wrong set of instructions. It it a typo at my end. Here is the correct set of instructions:

Use the graph to investigate limit of f(x) as
x→c. If the limit does not exist, explain why.
 
  • #12
phinds said:
see my EDIT
My apologies. I posted the correct problem with the wrong set of instructions. It it a typo at my end. Here is the correct set of instructions:

Use the graph to investigate limit of f(x) as
x→c. If the limit does not exist, explain why.
 

FAQ: Investigate Limit of Piecewise Function

1. What is a piecewise function?

A piecewise function is a mathematical function that is defined by multiple sub-functions, each of which is valid for a specific interval or "piece" of the domain. These sub-functions are usually connected by "breakpoints" or "transition points".

2. How do you determine the limit of a piecewise function?

To determine the limit of a piecewise function, you need to evaluate the limit of each sub-function at the given point. If the limits of all the sub-functions are equal, then that is the limit of the piecewise function. However, if the limits of the sub-functions are different, then the limit does not exist.

3. Can a piecewise function have a limit at a discontinuity?

No, a piecewise function cannot have a limit at a discontinuity. This is because the definition of a limit requires the function to approach the same value from both sides of the discontinuity, which is not possible for a piecewise function.

4. How do you graph a piecewise function?

To graph a piecewise function, you need to graph each sub-function separately on its respective interval and then connect the graphs at the breakpoints. It is also important to include an open or closed circle at the endpoint of each interval to indicate whether the endpoint is included in the graph or not.

5. Can a piecewise function be continuous?

Yes, a piecewise function can be continuous if the sub-functions are continuous and the breakpoints are also points of continuity. This means that the function is defined and has the same value at each breakpoint, and the limits from both sides of the breakpoint are equal.

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