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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: pHysiX on October 26, 2008, 07:29:02 pm

Title: Insight 2008 MM Exam1 Trial Error
Post by: pHysiX on October 26, 2008, 07:29:02 pm
Question 1 b):

the answer says loge|x-3|+4

however, if we look at the derivative function's domain, we see that it's (-infinity, 3). Therefore, the answer should be the negative reflection of the log, i.e.

loge(3-x)+4.

Please tell me if you agree with me because this type of question appeared in 2006 Sample Exams and they clearly solved it like that. =]
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: ReVeL on October 26, 2008, 07:35:57 pm
Wouldn't happen to have a version you could upload?

I've only got insight 2008 exam 2...
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: danieltennis on October 26, 2008, 07:37:53 pm
Godspeed.
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: danieltennis on October 26, 2008, 07:39:10 pm
Solutions
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: shinny on October 26, 2008, 08:14:24 pm
I don't think its necessarily an error, nor would you lose a mark for doing writing what they did, nor what you did; it's purely just a technicality. The domain restriction acts to give the answer you gave, but keeping the modulus has no difference in terms of the graph that is produced if you get what I mean, since the domain restriction still stays and produces what seems like .
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: pHysiX on October 26, 2008, 08:16:32 pm
mmm i agree with you there. but wen u look @ 2006 Sample Exam, I believe it's better to consider the other answer because it demonstrates that you understand functions etc. because really, the exams are about demonstrating knowledge.
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: riadnicolas on October 26, 2008, 08:21:24 pm
graphing the function might help you understand, compare gradient of modulus function and the derivative
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: shinny on October 26, 2008, 08:25:01 pm
Its the equivalent of cases where you have say, . The modulus is UNNECESSARY because the inside will always be greater than 0, but that doesn't mean it's wrong. Same with the case above; although the domain restriction implies that the inside of the modulus will always be negative, it doesn't mean its wrong to keep it there. But as you said, I would remove the modulus too and put the 'more correct' version just as insurance.
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: Mao on October 26, 2008, 09:38:25 pm
Quote from: pHysiX on October 26, 2008, 07:29:02 pm
Question 1 b):

the answer says loge|x-3|+4

however, if we look at the derivative function's domain, we see that it's (-infinity, 3). Therefore, the answer should be the negative reflection of the log, i.e.

loge(3-x)+4.

Please tell me if you agree with me because this type of question appeared in 2006 Sample Exams and they clearly solved it like that. =]

I gave the answer like you did, and you are correct.  However as other people have said, there is also a domain restriction.  This makes the modulus log function also correct.  On a VCAA exam, I'd write it how you did OR use the modulus log, however re-write the domain of the function, next to your answer, so they know you've limited it [as required in the question].

P.S. This isn't Mao.
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: Glockmeister on October 26, 2008, 10:13:50 pm
Quote
P.S. This isn't Mao.

Huh? Has he finally manage to divide by zero?
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: amycourty on October 27, 2008, 02:33:44 pm
would anyone happen to have the insight 2008 exam 2 and be willing to share with me?  :angel:

Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: Chocoholic on October 27, 2008, 02:43:17 pm
jess posted it in this thread :)
http://vcenotes.com/forum/index.php/topic,6375.15.html
Title: Re: Insight 2008 MM Exam1 Trial Error
Post by: amycourty on October 27, 2008, 05:32:54 pm
thanks muchly