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February 1, 2015

February 1, 2015

Posted by **W** on Monday, November 21, 2011 at 12:12am.

Thanks for your help!

- Calculus -
**Steve**, Monday, November 21, 2011 at 4:46amI think you may be going about things backwards. If

u = 3/x

du = -3/x^2 dx

and your integrand becomes e^u du/(-3) = -1/3 Int(e^u du) = -1/3 e^u = -1/3 e^3/x

check: taking the derivative of -1/3 e^3/x we get

-1/3 * e^3/x * -3/x^2 = e^(3/x) / x^2

So, evaluating at 3 and 1,

-1/3 e^(3/3) + 1/3 e^(3/1) = 1/3 (e^3 - e)

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