# Thread: What I dont understand is

1. ## 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?

2. 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.

$\int_a^b e^{-x^2}\, dx = \frac{\sqrt{\pi}}{2} (\text{erf} (b) - \text{erf} (a))$.

3. ## 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...