# bell curve

• Jul 18th 2007, 04:35 PM
Quick
bell curve
small question, is there an equation that'll give you a graph like a bell curve?
• Jul 18th 2007, 05:43 PM
galactus
Yes, there is:

The one used to calculate the standard normal table is:

$\displaystyle \frac{1}{\sqrt{2\pi}}\int_{-\infty}^{z}{e^{\frac{-x^{2}}{2}}}dx$

For instance, if you have a stats book with the table to compare for fun.

Try integrating the above with z=-1.645. You should get very close to 0.05.

Actually, it's 0.0499849....
• Jul 18th 2007, 07:05 PM
ThePerfectHacker
Quote:

Originally Posted by Quick
small question, is there an equation that'll give you a graph like a bell curve?

Are you interested to know why there is a factor of $\displaystyle 2\pi$ there?
• Jul 25th 2007, 06:21 AM
Quick
Quote:

Originally Posted by ThePerfectHacker
Are you interested to know why there is a factor of $\displaystyle 2\pi$ there?

No, I just wanted to see how to mess with the curve :o
• Jul 25th 2007, 08:15 AM
CaptainBlack
Quote:

Originally Posted by Quick
small question, is there an equation that'll give you a graph like a bell curve?

Normal density:

$\displaystyle f(x)=\frac{1}{\sqrt{2 \pi} \sigma} e^{-\frac{(x-\mu)^2}{2 \sigma^2}}$

RonL