# What I dont understand is

• Mar 31st 2008, 06:30 PM
Mathstud28
What I dont understand is
After deriving "erf(x)" with Maclaurin series...I am still oblivous as to two things...where to 2/pi^(1/2) came from and as to say if I was integrating e^(-x²) from 4 to 2 how I would plug in numbers into erf(x) to acheive the numerical answer? Could someone help?
• Mar 31st 2008, 06:51 PM
mr fantastic
Quote:

Originally Posted by Mathstud28
After deriving "erf(x)" with Maclaurin series...I am still oblivous as to two things...where to 2/pi^(1/2) came from and as to say if I was integrating e^(-x²) from 4 to 2 how I would plug in numbers into erf(x) to acheive the numerical answer? Could someone help?

2/pi^(1/2) is a constant that is introduced so that erf(+oo) = 1. There are good reasons for doing this.

$\int_a^b e^{-x^2}\, dx = \frac{\sqrt{\pi}}{2} (\text{erf} (b) - \text{erf} (a))$.
• Mar 31st 2008, 06:57 PM
Mathstud28
Hmm
That is what I thought obviously since F(b)-F(a) where F'(x)=f(x) but I swore I did it and got the wrong values...