# Homework Help: How is this question solved?

1. Jun 12, 2010

### I dun get it

[PLAIN]http://img517.imageshack.us/img517/6328/q75c.gif [Broken]

I know that you have to substitute u=2x+1 into the second equation, but I don't know where to go from there.

Last edited by a moderator: May 4, 2017
2. Jun 12, 2010

### Gregg

Let $$\int f(x) dx = F(x)$$

then $$\int ^3_{-1} f(x) dx = F(3) - F(-1) = 12$$

so $$\int^1_{-1} f(2x+1) dx = ?$$

3. Jun 12, 2010

### I dun get it

The answer given is 6, whereas that gives me 12.

4. Jun 12, 2010

### Dick

Try actually doing the substitution. If u=2x+1, what's the relation between dx and du?

5. Jun 12, 2010

### I dun get it

Oh, I get it now.

6. Jun 13, 2010

### Staff: Mentor

So now you'll need to change your user name.