log derivatives

**viet** · June 5th, 2007, 06:22 PM

can someone check if I'm doing this right:

1.) $\frac{d}{dx} \int^{3x+2}_1 \frac{1}{t}dt$

$\frac{d}{dx} ln(3x+2)$

$\frac{1}{3x+2}*3$

ans: $\frac{3}{3x+2}$
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2.) $\int\big(\frac{d}{dx} lnf(x)\big)dx$

$\int \frac{1}{f(x)}dx$

ans: $lnf(x) + C$

**ThePerfectHacker** · June 5th, 2007, 06:38 PM

Originally Posted by viet

can someone check if I'm doing this right:

1.) $\frac{d}{dx} \int^{3x+2}_1 \frac{1}{t}dt$

$\frac{d}{dx} ln(3x+2)$

$\frac{1}{3x+2}*3$

ans: $\frac{3}{3x+2}$

This looks correct to me, even after I had 6 shots of whiskey. What was I saying again?

2.) $\int\big(\frac{d}{dx} lnf(x)\big)dx$

$\int \frac{1}{f(x)}dx$

ans: $lnf(x) + C$

But no need to do all that.
You should not that the integral of the derivative is the original function plus constants. Since the original function was $\ln f(x)$ means the the answer would be $\ln f(x) +C$ .

**curvature** · June 6th, 2007, 05:52 AM

Originally Posted by viet

can someone check if I'm doing this right:

2.) $\int\big(\frac{d}{dx} lnf(x)\big)dx$

$\int \frac{1}{f(x)}dx$

ans: $lnf(x) + C$

On the 2nd question

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