# Homework Help: Evaluate the integral

1. Aug 3, 2010

### Kinetica

1. The problem statement, all variables and given/known data

integral:

x2 sqrt(2+x3) dx

2. Relevant equations

3. The attempt at a solution

Should I use substitution? Should I do it as a power?

2. Aug 3, 2010

### Bohrok

U substitution is the way to go for this one.

3. Aug 4, 2010

### HallsofIvy

Since the only difficulty is that "$2+ x^3$" inside the square root, let $u= 2+ x^3$ seems an obvious way to go.

4. Aug 4, 2010

### Kinetica

So when I substitute it as HallsofIvy suggested, what do I do with x2dx?
x2dx=du?

integral:
sqrt(u)du=2u3/2/3......

stuck.

5. Aug 4, 2010

### Dick

If u=2+x^3 isn't du=3*x^2*dx? Isn't that how substitution works?

6. Aug 4, 2010

### Kinetica

I am extremely confused with the next step of the solution.

integral
sqrt(u)du/(3x2) is this the correct substitution?

7. Aug 4, 2010

### Dick

Well, no. What happened to the x^2 in your original problem? Isn't it x^2*sqrt(u)*(du/(3*x^2))?

8. Aug 4, 2010

### Kinetica

Thanks goodness, I got it.