Putting an absolute value sign around a log? (1 Viewer)

[~ ReNcH ~]

When differentiating/integrating etc. and your final answer is a log, should you express the result as an absolute value?
E.g. instead of ln(cosx), putting ln(|cosx|)

Should this be done in all cases involving logs? Is it better to use them to be on the safe side? Suppose we don't express the log as a modulus, would we be marked down?

 

[Captain pi]

When a primitive results in a logarithmic function, you should enclose the argument with absolute value signs.

You will never be required, in Extension 1, to place absolute value enclosures around logarithmic arguments.

I believe they may question you, in 3U, on the domain of logarithmic functions; therefore, never (except in integration) place absolute value enclosures without justification.

Thus,

ln(x) remains ln(x); not ln|x|, unless this is a primitive function.

 

[Ogden_Nash]

Regarding log functions in definite integrals, you can actually prove that ln(-x) will produce the same result as ln(x). However, this requires knowledge of Euler's formula and that's why absolute values are more encouraged in 4u.

 

[FinalFantasy]

ext. 1 doesn't matter
ext. 2 they expect u to put absolute value signs on da log thingy and remove them only when u can prove dat the thing is +VE

 

[~ ReNcH ~]

ext. 1 doesn't matter
ext. 2 they expect u to put absolute value signs on da log thingy and remove them only when u can prove dat the thing is +VE

Ah ic.
So if the expression within the log can be either negative or positive or you don't know for sure, then use the absolute value sign?

 

[FinalFantasy]

Ah ic.
So if the expression within the log can be either negative or positive or you don't know for sure, then use the absolute value sign?

yea, always put absolute value sign on da log thing, but always try to get rid of them though, like always look for a reason y it must be +ve den get rid of it whenever u can

 

[~ ReNcH ~]

In a question where the use of the absolute value is important in answering following parts or in establishing a principle, I can understand that you might be marked down for failing to use them. Although, I wonder if you'd be marked down for failing to use absolute value signs in a standard integration question.