stupid math question.

[yoda291]

Hello all,

Took an online test and the answer key isn't correlating to a textbook example so I kind of need a third opinion on a simple limit question.

whatis
lim x->2 for
x^2 + 2x + 1 ?

 

[Born2bwire]

Uhhh.... 9?

 

[BrownTown]

why in the hell would you use a limit for something like that?

 

[Cogman]

Originally posted by: BrownTown
why in the hell would you use a limit for something like that?

Probably just to test the test takers knowledge on what a limit is.

(as was stated the limit from both the right and left is 9)

 

[presidentender]

Originally posted by: Cogman

Originally posted by: BrownTown
why in the hell would you use a limit for something like that?

Probably just to test the test takers knowledge on what a limit is.

(as was stated the limit from both the right and left is 9)

Yeah, same as the value of the function. This has to be a very basic calc course.

 

[Calculator83]

hahahahahaha.... n000b.

 

[BassBomb]

Highly Technical lol

 

[firewolfsm]

Basically, if X approaches 2, treat it as 2.

 

[yoda291]

Originally posted by: BassBomb
Highly Technical lol

I didn't know where else to put it!



PS - the reason I asked is that the answer key says the answer is 7 and I haven't the foggiest notion as to where 7 came from.

 

[TKE899]

Your answer key is wrong. That is the facts.

 

[Cogman]

Originally posted by: yoda291

Originally posted by: BassBomb
Highly Technical lol

I didn't know where else to put it!



PS - the reason I asked is that the answer key says the answer is 7 and I haven't the foggiest notion as to where 7 came from.

are you sure it isn't a misprinted 9? If the loop didn't finish they may look similar (That or the person typing it in wasn't paying attention/didn't know better)

 

[degibson]

42

 

[Calculator83]

Originally posted by: Cogman

Originally posted by: yoda291

Originally posted by: BassBomb
Highly Technical lol

I didn't know where else to put it!



PS - the reason I asked is that the answer key says the answer is 7 and I haven't the foggiest notion as to where 7 came from.

are you sure it isn't a misprinted 9? If the loop didn't finish they may look similar (That or the person typing it in wasn't paying attention/didn't know better)

OP clearly not gonna be a scientist. We could sleep easy that he's not building our bridges. Op needs to download the TI89 emulator to solve his problems

 

[Net]

as x approaches 2. 2^2 + 2(2) + 1

 

[DrPizza]

Originally posted by: BrownTown
why in the hell would you use a limit for something like that?

To check for understanding of what a limit is? Sometimes students get so caught up in the methods that when you toss them a really easy problem, they choke - showing they've memorized all the techniques for harder problems, but really don't understand what they're doing. Take 100 students who have taken a test that includes L'Hopital's rule, and give them this question: lim x->2 of (x²+3x-5)/(x²-2x+3), and a significant number of them will apply L'Hopital's rule improperly.

 

[cusideabelincoln]

The simplest answer as to why your answer didn't match is because somebody made a mistake. Either the answer was typed in wrong, the expression was typed in wrong (x^2 + 2x -1), or whoever put the test up didn't double check his or her work, e.g. maybe they actually found the limit for x->2 | x^2 + 2x - 1 to get 7.

 

[TuxDave]

Originally posted by: DrPizza

Originally posted by: BrownTown
why in the hell would you use a limit for something like that?

To check for understanding of what a limit is? Sometimes students get so caught up in the methods that when you toss them a really easy problem, they choke - showing they've memorized all the techniques for harder problems, but really don't understand what they're doing. Take 100 students who have taken a test that includes L'Hopital's rule, and give them this question: lim x->2 of (x²+3x-5)/(x²-2x+3), and a significant number of them will apply L'Hopital's rule improperly.

lol it must've been a while since I had to work with that. I still remember what L'Hopital's rule and when you needed to apply it. I guess I never put that much thought about when you're NOT supposed to apply it. Oh how my brain quickly shrivels away after graduation....

 

[mathminded]

Originally posted by: firewolfsm
Basically, if X approaches 2, treat it as 2.

In the case of functions that are defined on a close interval [a,b] and continuous on (a,b) where a<x<b, yes. Otherwise, this advise leads to false statements fast.

Simple example of this advice failing: compute the limit as x approaches 0 of f(x) = 1/x, where x is any negative real number.