Finding parameter m from left and right limits

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CallMeShady
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Homework Statement


Problem statement: piecewise function f(x) equals 8x cubed minus 2m for x less than or equal to -1, and 7x squared plus 5m for x greater than -1, with three parts asking for one-sided limits and a value of m making them equal.



Homework Equations


Only ones I know that are relevant are the equations shown in the question (for the left and right limits).


The Attempt at a Solution


The difficulty that I am having right not is comprehending what is really being asked from the question. From what I understand, then question is asking the "m" values from the left and right limits at the top, and the value for "m" when those limits are the same. However, how would I go about finding the value of "m" if I have no x or y co-ordinates given?
 
CallMeShady said:

Homework Statement


Piecewise definition of f(x): 8x^3 - 2m for x ≤ -1 and 7x^2 + 5m for x > -1, with three parts asking for lim as x→-1+ and x→-1- of f(x) and for values of m making the one-sided limits equal.



Homework Equations


Only ones I know that are relevant are the equations shown in the question (for the left and right limits).


The Attempt at a Solution


The difficulty that I am having right not is comprehending what is really being asked from the question. From what I understand, then question is asking the "m" values from the left and right limits at the top, and the value for "m" when those limits are the same. However, how would I go about finding the value of "m" if I have no x or y co-ordinates given?
What is [itex]\displaystyle \lim_{x\to\,1}(8x^3-2m)\ ?[/itex]
 
SammyS said:
What is [itex]\displaystyle \lim_{x\to\,1}(8x^3-2m)\ ?[/itex]

That is not given (everything above that I posted is the only thing given). Or are you suggesting that I should calculate that to solve this problem. That expression just defines the limit from the left side. I am unsure on how to calculate that.
 
CallMeShady said:
That is not given (everything above that I posted is the only thing given). Or are you suggesting that I should calculate that to solve this problem. That expression just defines the limit from the left side. I am unsure on how to calculate that.
What do you mean, it's not given?

I'm asking you to evaluate the limit, [itex]\displaystyle \lim_{x\to\,1}(8x^3-2m)\,,[/itex] if you can. If you can't, I don't how you can do this problem at all.
 
SammyS said:
What do you mean, it's not given?

I'm asking you to evaluate the limit, [itex]\displaystyle \lim_{x\to\,1}(8x^3-2m)\,,[/itex] if you can. If you can't, I don't how you can do this problem at all.


I don't see how I can evaluate that limit... I could isolate "m" though by temporarily assigning "f(x)" as "y". Then I could isolate "m" in terms of "y" => "m(y)".
 
Sammy is not asking you to solve for m (i.e., isolate me) - just evaluate the limit, which by the way should be
$$\lim_{x \to -1^{-}}(8x^3 - 2m) $$

Your answer should be in terms of m.
 
CallMeShady said:
I don't see how I can evaluate that limit... I could isolate "m" though by temporarily assigning "f(x)" as "y". Then I could isolate "m" in terms of "y" => "m(y)".
[itex]\displaystyle \lim_{x\to\,1}(8x^3-2m) = 8(1)^3-2m=8-2m[/itex]

That's all there is to it !
 
I can't believe how easy this question actually was... I was making it too complex due to the fact that I wasn't comprehending this question very well. A sincere thank you to Mark and Sammy for their assistance. I really appreciate it.
 
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CallMeShady said:
I can't believe how easy this question actually was... I was making it too complex due to the fact that I wasn't comprehending this question very well. A sincere thank you to Mark and Sammy for their assistance. I really appreciate it.

So, what are you results?