# Find this integral

1. Oct 26, 2011

### arslan894

f(x) = ∫e^(1-(x^2)/(b^2))dx the limits are -b to b , take the value of b = 3

2. Oct 26, 2011

### DivisionByZro

Is this the integral?
$$\int_{-3}^{3}e^\frac{1-x^2}{9}dx$$

3. Oct 26, 2011

### phyzguy

We're not going to do it for you. What have you tried?

4. Oct 26, 2011

### arslan894

bro i tried it using substitution but the problem is that i cant go much further, @ DivisionByZro exp(1-(x^2/9))^.5

5. Oct 26, 2011

### DivisionByZro

Is this it?
$$\int_{-3}^{3}e^\sqrt{1-\frac{x^2}{9}}dx$$

6. Oct 26, 2011

### arslan894

yes bro

7. Oct 26, 2011

### DivisionByZro

Well, in any case, you won't find any substitutions since you don't have any "x" term multiplying the expression, therefore whatever you have in the exponent part can't be reduced. In other words, it wouldn't be as hard if your integral was something like:

$$\int_{-3}^{3}xe^{x^{2}}dx$$

In this case if you let u=x2, then du=2xdx, and you could use substitution.

8. Oct 26, 2011

### arslan894

i was modeling in matlab to find the friction between cam follower of an engine ,i used int function in matlab but it gave warning that explicit answer doesnt exist ,i used the simpson 38 rule to find the solution on paper but dont know how to use simpson 38 rule in matlab.

9. Oct 26, 2011

### arslan894

any one knows how to do this function using simpson 3 8 rule in matlab ?

10. Oct 26, 2011

### phyzguy

11. Nov 18, 2011

### bhartish

I also have a doubt . Anybody reply fast

How to integrate

exp(x)*erfc(x) in MATLAB