intergration question (1 Viewer)

[utopia_parkway]

the question was
/ 5t^2+3 (1996HSC, Q1,c)
| t(t^2+1)
/

and the answer i got was log(t^3+1) +2log(t) + C

however in the answer booklet they had absolute value signs insted of ()
i.e log|t^3+1|+2log|t| + C

do i have to put absolute valus signs or not.


thanks

 

[grimreaper]

Hmm I'm not sure if they HAVE to be in there to get full marks, but technically they should be. Does anyone else know for certain whether the absolute value signs need to be in?

 

[cj_bridle]

im pretty sure its acceptable just to have the ( ) .
you wouldnt get marked down. they are trying to give marks remember not take them away.

 

[utopia_parkway]

but if you change the () to || it means that the log is defined for every number which means that you could find the area below a curve below where the curve is undefined.

 

[Mill]

In HMX2 you are supposed to put the absolute value signs.

In HM and HMX1, the normal brackets usually suffice.

 

[townie]

i always put the || in as a matter of course, because a log has to be positive

 

[Xayma]

but if you change the () to || it means that the log is defined for every number which means that you could find the area below a curve below where the curve is undefined.

Except for t=-1 or t=0

 

[mojako]

yep, you can put (...)

> but if you change the () to || it means that the log is defined for every number which means that you could find the area below a curve below where the curve is undefined. <
the curve is defined everywhere.. except at the two points mentioned by Xayma.

 

[xiao1985]

yep, you can put (...)

> but if you change the () to || it means that the log is defined for every number which means that you could find the area below a curve below where the curve is undefined. <
the curve is defined everywhere.. except at the two points mentioned by Xayma.

i doubt it... if u get logs out of integration, if u put || u will not be wrong, whereas, if u have (), u maybe marked down... at least marker have reasons to mark u down...

 

[dawso]

yeah, i suppose its just one of those things like puttin correct reasons on geometry questions, u wont get marked down if u do do it and u neva know, u mite if ya dont, u may aswell put it cause it dont use much time
-dawso

 

[dawso]

yeah, i suppose its just one of those things like puttin correct reasons on geometry questions, u wont get marked down if u do do it and u neva know, u mite if ya dont, u may aswell put it cause it dont use much time
-dawso

 

[nike55]

heres a decent alternate solution

/ 5t^2+3 (1996HSC, Q1,c)
| t(t^2+1)
/

= I_n (5t⁴+3t²) / (t⁵ + t³) (times num/ denom by t^2/t^2)
= log_e(t⁵ + t³)

 

[Rorix]

ln (t^5 + t^3) = ln (t^2(t^3+1) = ln t^2 + ln t^3+1 = 2lnt + ln(t^3 +1)
+ c

 

[CrashOveride]

ln (t^5 + t^3) = ln (t^2(t^3+1)

Perhaps you mean ln(t^3(t^2+1))

 

[Rorix]

*goes off to cry*

 

[spaz1810]

in a standard integration question you should put the |...| as this is the true answer. however in cases like resisted motion and other mechanics questions the section in the brackets is usually positive (eg in resisted motion g-kv > 0) in this case you should leave the |...| off otherwise you need to justify their removal later when only using the positive and disregarding the negative

 

[~MC MATAR~]

You Have To Put The Absolute Value Signs Because A Log Is Undefined For A Negative Number. Ext 1 Students Let Alone Extension 2 Students Should Be Able To Recognise This. This Way All Values Of X Are Included In The Integrand

 

[mojako]

You Have To Put The Absolute Value Signs Because A Log Is Undefined For A Negative Number. Ext 1 Students Let Alone Extension 2 Students Should Be Able To Recognise This. This Way All Values Of X Are Included In The Integrand

Ext1 students are NOT expected to write the absolute value sign.
Many of them are in fact never told by their teachers about the idea of taking absolute values.

 

[Jase]

You Have To Put The Absolute Value Signs Because A Log Is Undefined For A Negative Number. Ext 1 Students Let Alone Extension 2 Students Should Be Able To Recognise This. This Way All Values Of X Are Included In The Integrand

Why Did You Type Like That?

 

[Supra]

perhaps for emphasis