When integrating to ln/log... (1 Viewer)

[trecex1]

Will not putting absolute value around what is inside ln/log lose marks? When do/don't you put it instead of just regular bracket? Eg. Indefinite integral of tanxdx = -ln(cosx)+c or -ln|cosx| + c? Seen some solutions that use abs and some with brackets, also some just don't put anything eg. integral of 1/x = lnx . Can someone let me know ty.

 

[Paradoxica]

Will not putting absolute value around what is inside ln/log lose marks? When do/don't you put it instead of just regular bracket? Eg. Indefinite integral of tanxdx = -ln(cosx)+c or -ln|cosx| + c? Seen some solutions that use abs and some with brackets, also some just don't put anything eg. integral of 1/x = lnx . Can someone let me know ty.

My teacher says that it is entirely possible that marks will be deducted if you do not place the absolute values because that is what it says in the Syllabus. So for safety's sake, just always put the absolute values.

Even if the function in question is positive.

 

[leehuan]

My teacher says that it is entirely possible that marks will be deducted if you do not place the absolute values because that is what it says in the Syllabus. So for safety's sake, just always put the absolute values.

Even if the function in question is positive.

Only for Extension 2.

At Extension 1 level, the absolute values can safely be omitted.
_______

As for ln(cos x) v.s. ln cos x
and ln(x) v.s. ln x

Depending on what the answer is, the one with brackets will either make things CLEARER (first one), or just waste 1 second of your life (second one)

 

[InteGrand]

My teacher says that it is entirely possible that marks will be deducted if you do not place the absolute values because that is what it says in the Syllabus. So for safety's sake, just always put the absolute values.

Even if the function in question is positive.

Where did it say that in the Syllabus (not saying it didn't, but I had a quick skim through the Integration part of the 4U Syllabus and couldn't see it there. Might've missed it or could be in the 2U/3U Syllabus.)?

 

[Paradoxica]

Where did it say that in the Syllabus (not saying it didn't, but I had a quick skim through the Integration part of the 4U Syllabus and couldn't see it there. Might've missed it or could be in the 2U/3U Syllabus.)?

Technically not in the Syllabus, but the Table of Standard Integrals, although with the new changes introduced not sure what is happening anymore.

 

[InteGrand]

Technically not in the Syllabus, but the Table of Standard Integrals, although with the new changes introduced not sure what is happening anymore.

Had a look at the HSC's table of Standard Integrals, and what they did for the integral of 1/x was write it as "ln x, x > 0", rather than "ln |x|".

(The table can be found at the end of last year's HSC MX2 exam paper, for instance: https://www.boardofstudies.nsw.edu.au/hsc_exams/2015/exams/2015-hsc-maths-ext-2.pdf .)

 

[leehuan]

Yeah the table left it as ln x

The new reference sheet awkwardly puts it out but when I stopped by my old school, I asked one of the teachers (pretty sure she's well known within MANSW) and she commented on how it still wasn't necessary.

 

[InteGrand]

Yeah the table left it as ln x

The new reference sheet awkwardly puts it out but when I stopped by my old school, I asked one of the teachers (pretty sure she's well known within MANSW) and she commented on how it still wasn't necessary.

What do you mean 'puts it out' (haven't got the new Reference Sheet handy)? As in it writes it with absolute value signs?

(Edit: OK here's the link to the new Reference Sheet: http://www.boardofstudies.nsw.edu.au/syllabus_hsc/pdf_doc/maths-ref-sheet.pdf .)

 

[leehuan]

What do you mean 'puts it out' (haven't got the new Reference Sheet handy)? As in it writes it with absolute value signs?

(Edit: OK here's the link to the new Reference Sheet: http://www.boardofstudies.nsw.edu.au/syllabus_hsc/pdf_doc/maths-ref-sheet.pdf .)

I feel it's awkward because that's saying dear 2U put the absolute values sign in.

When I really don't think it matters for them

 

[InteGrand]

I feel it's awkward because that's saying dear 2U put the absolute values sign in.

When I really don't think it matters for them

Maybe BOSTES didn't want to put that formula in twice (one with an absolute value and one without), so decided to put in the absolute value one only (like if you had to choose to put only one, that'd probably be the one to choose).

 

[integral95]

Yeah I don't think they would actually deduct marks for that, but if you had to compute a definite integral with negative limits, then you'd have to include the absolute value.