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Q. `int log_ex dx` A) `log_e(|x| - 1) + c` B) `(log_e|x|)/x - 1 + c` C) ` `...

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user8235304 | Student, Grade 11 | Valedictorian

Posted August 13, 2013 at 11:57 AM via web

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Q. `int log_ex dx`

A) `log_e(|x| - 1) + c`

B) `(log_e|x|)/x - 1 + c`

C) ` ` `x(log_e(|x| - 1)) + c`

D) `1/x + log_e|x| + c`

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embizze | High School Teacher | (Level 1) Educator Emeritus

Posted August 13, 2013 at 12:16 PM (Answer #1)

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Find `int lnx dx`   **lnx is the natural logarithm or `log_e x` **

Use integration by parts:

`int udv=uv-intvdu`

Let `u=lnx, du=1/x dx,v=x,dv=dx`

`int lnx dx=xlnx-int x(1/x dx)`

`=xlnx-int dx`

`=xlnx-x+C` where C is an arbitrary constant.

(Alternative representation x(lnx-1)+C )

Sources:

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embizze | High School Teacher | (Level 1) Educator Emeritus

Posted August 13, 2013 at 12:20 PM (Reply #1)

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Of the answers provided, C would be correct. Is there a typo in the answer? (Should not be x(ln(|x|-1)); should be x(ln|x|-1) )

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