# find the integral(2)

• Mar 9th 2010, 04:46 AM
chialin4
find the integral(2)
1.$\displaystyle \int\frac{sinx}{x}dx$
2.$\displaystyle \int_{-00}^{00} (cosx)e^{-x^{2}/2}dx$
• Mar 9th 2010, 04:48 AM
shawsend
Quote:

Originally Posted by chialin4
$\displaystyle \int\frac{sinx}{x}dx$

$\displaystyle \int \frac{\sin(x)}{x}dx=\text{SinIntegral(x)}$

. . . stop special function discrimination: equal rights for special functions.
• Mar 9th 2010, 05:13 AM
chialin4
Quote:

Originally Posted by shawsend
$\displaystyle \int \frac{\sin(x)}{x}dx=\text{SinIntegral(x)}$

. . . stop special function discrimination: equal rights for special functions.

???
what do u mean ?
• Mar 9th 2010, 05:20 AM
Miss
Quote:

Originally Posted by chialin4
???
what do u mean ?

You can not solve this integrals in terms of elementary function.
This well-known integral is used in electrical engineering.
See:
integrate sin&#x28;x&#x29;&#x2f;x - Wolfram|Alpha
• Mar 9th 2010, 07:23 AM
shawsend
Quote:

Originally Posted by chialin4
???
what do u mean ?

Hi. It's a suggestion to treat "special functions" like antiderivatives of integrals that can't be expressed in simple terms, in the same way that you treat $\displaystyle \sin(x)$ so if I have $\displaystyle \int \cos(x)dx$ you say "hey, that's easy, it's $\displaystyle \sin(x)$. So hey, $\displaystyle \int \frac{sin x}{x}$ is easy. It's . . .

Also, for that second we did that one here:

http://www.mathhelpforum.com/math-he...x-e-x-2-a.html