Integral [example thread of why you should post all given info]

**chengbin** · June 11th 2009, 05:28 PM

This thread is now changed to ask people to remember to post the whole question instead of one part. It saves time and confusion.

Thank you.

Original question (look at this as an example)

How do you integrate this function?

$\int \frac {\cos x}{x} dx$

**Random Variable** · June 11th 2009, 05:32 PM

The antiderivative cannot be expressed in terms of elementary functions.

**chengbin** · June 11th 2009, 05:43 PM

The question is

Suppose for a certain function f it is known that

$f'(x)=\frac {\cos x}{x}$ , $f(\frac {\pi}{2})=a$ and $f(\frac {3\pi}{2})=b$

Use integration by parts to evaluate

$\int_\frac{\pi}{2}^\frac{3\pi}{2} f(x) dx$

**Random Variable** · June 11th 2009, 06:12 PM

$\int_\frac{\pi}{2}^\frac{3\pi}{2} f(x) dx = xf(x) \Big|^{\frac{3\pi}{2}}_{\frac{\pi}{2}} - \int^{\frac{3\pi}{2}}_{\frac{\pi}{2}} xf'(x) \ dx$

$= xf(x) \Big|^{\frac{3\pi}{2}}_{\frac{\pi}{2}} - \int^{\frac{3\pi}{2}}_{\frac{\pi}{2}} cos(x) \ dx$

**mr fantastic** · June 12th 2009, 03:10 AM

This is an excellent thread for showing why it's important to post the whole question, not just the bits of the question that seem important.

**chengbin** · June 12th 2009, 03:14 AM

I kind of wanted to do the question myself, and ask for help only on the part I'm stuck on.

**mr fantastic** · June 12th 2009, 03:24 AM

Originally Posted by chengbin

I kind of wanted to do the question myself, and ask for help only on the part I'm stuck on.

Then you should post the whole question, show what you've done, say where your stuck and then state that you want only a hint rather than the whole solution.

**chengbin** · June 12th 2009, 07:31 AM

Will do.

Thread: Integral [example thread of why you should post all given info]

LinkBack

Thread Tools

Display

Integral [example thread of why you should post all given info]

Why it's important to post the whole question, not just the bits that seem important

Similar Math Help Forum Discussions

Getting Less info same stat as more info

Tricky integral question..need a little info..

Search Tags