# Homework Help: Approximate integration

1. Apr 29, 2009

### Matterwave

1. The problem statement, all variables and given/known data
This is technically an E&M question, but I've reduced it to a calculus problem. Basically I have to evaluate:

$$B_0(\int_{-H_{max}}^{H_{max}}{tanh(\frac{H+H_c}{H_0})dH - \int_{-H_{max}}^{H_{max}}{tanh(\frac{H-H_c}{H_0})dH)$$

Where $$H_{max}>>H_C, H_0$$.

2. Relevant equations

3. The attempt at a solution

I'm looking at this and I have no idea how to go about approximating this integral...I suppose I could just brute force the integrals and keep all the H_max and stuff, and then later see if i can approximate something...but the expressions are really quite long and I'd like to avoid that if I can. Is there a way?

2. Apr 29, 2009

### tiny-tim

Hi Matterwave!

Are Hc and H0 constants?

If so, that's just ∫tanh(Ax + b) dx …

and ∫tanh is ln(cosh)

3. Apr 29, 2009

### D H

Staff Emeritus
You can eliminate the second integral (it's just the additive inverse of the first; prove it). Per tiny-tim's hint, you can compute the integral. Simplify and finally use the fact that Hmax>>Hc , H0 to arrive at an approximate value.