How to Solve an Equation with a Substitution Method?

[I dun get it]

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

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

 

[Gregg]

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

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

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

 

[I dun get it]

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

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

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

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

 

[Dick]

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

 

[I dun get it]

Oh, I get it now.

 

[Mark44]

Oh, I get it now.

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