find this integral

[arslan894]

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

[DivisionByZro]

Is this the integral?

\int_{-3}^{3}e^\frac{1-x^2}{9}dx

[phyzguy]

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

[arslan894]

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

[DivisionByZro]

Is this it?

\int_{-3}^{3}e^\sqrt{1-\frac{x^2}{9}}dx

[arslan894]

yes bro

[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.

In fact there is no answer in terms of standard functions. What class/context was this for?

[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.

[arslan894]

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

[phyzguy]

I don't know Matlab, but you can numerically integrate this function on Wolfram Alpha, and it gives 13.46. It even plots it out for you. Here's the link:

http://www.wolframalpha.com/input/?i=NIntegrate[Exp[Sqrt[1-x^2/9]],{x,-3,3}]

[bhartish]

I also have a doubt . Anybody reply fast


How to integrate

exp(x)*erfc(x) in MATLAB