# Homework Help: Any help will be appreciated assuming a pretty easy integral

1. Jan 17, 2012

### IntegrateMe

Any help will be appreciated...assuming a pretty easy integral....

∫f(t) dt = 9 [0, 1]

Find:

∫f(10t)dt [0, 0.1]
∫f(1 - 10t)dt [0, 0.1]

Any idea on how to get started with this one?

2. Jan 17, 2012

### Dick

Re: Any help will be appreciated...assuming a pretty easy integral....

Change variables with a u-substitution. For the first one try u=10t. What is du?

3. Jan 17, 2012

### IntegrateMe

Re: Any help will be appreciated...assuming a pretty easy integral....

10dt!

4. Jan 17, 2012

### Dick

Re: Any help will be appreciated...assuming a pretty easy integral....

Ok, so change the t integral to a u integral.

5. Jan 17, 2012

### IntegrateMe

Re: Any help will be appreciated...assuming a pretty easy integral....

1/10∫f(u)du ?

6. Jan 17, 2012

### Dick

Re: Any help will be appreciated...assuming a pretty easy integral....

Looks good so far. And what are the u limits? The t limits were [0,0.1].

7. Jan 17, 2012

### IntegrateMe

Re: Any help will be appreciated...assuming a pretty easy integral....

From 0 to 0.1.

Does ∫f(u)du = 9?

8. Jan 17, 2012

### Dick

Re: Any help will be appreciated...assuming a pretty easy integral....

It won't be 9, if the u limits are 0 to 0.1. But they aren't. If t=0.1, what's the corresponding u?