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March 22nd, 2015, 04:18 AM  #1 
Newbie Joined: Mar 2015 From: Romford Posts: 8 Thanks: 0  how reliable are online integration calculators
As I'm studying alone, I sometimes need online tools to check my calculations. But I noticed some inconsistency with online integration calculators. For the expression 15/(2x450) I got different answers from two different calculators. Integral Calculator: Wolfram Mathematica Online Integrator 15/2*ln(4502x) from Wolfram Online Integral Calculator • Find Integrals and Antiderivatives! 15/2*ln(2x450) from this one Did I read something wrong, or are they giving me different results? Seb 
March 22nd, 2015, 06:01 AM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 3,034 Thanks: 1621 
Actually, they're both correct ... and both incorrect. Should be ... $\displaystyle \int \frac{15}{2x450} \, dx = \frac{15}{2}\ln2x450 +C$ The one you accept as correct depends if $2x450 >0$ or if $4502x>0$. That is why absolute value of the log argument is necessary if you don't know which of the above is true. Note $2x450=4502x$ takes care of either situation. 
March 22nd, 2015, 06:08 AM  #3 
Math Team Joined: Jul 2011 From: Texas Posts: 3,034 Thanks: 1621 
Also, check out the result my TI CAS gives ...

March 22nd, 2015, 06:24 AM  #4 
Newbie Joined: Mar 2015 From: Romford Posts: 8 Thanks: 0 
Sorry I'm still rather a beginner at calculus, how does it get to x225? Seb 
March 22nd, 2015, 04:25 PM  #5 
Math Team Joined: Jul 2011 From: Texas Posts: 3,034 Thanks: 1621  

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