# Homework Help: Double integral yx

1. May 23, 2010

### SimpliciusH

Last edited by a moderator: May 4, 2017
2. May 23, 2010

### gabbagabbahey

No, you are integrating over both $y$ and $x$, so your answer shouldn't have $x$ in it. Why not show us your steps...

Last edited by a moderator: May 4, 2017
3. May 23, 2010

### hgfalling

His x limit of integration includes an x, so I think this is the right answer. I suspect it might be the wrong integral, however. :)

4. May 23, 2010

### SimpliciusH

Ok, I'll post the steps... BTW Can I just ask how one writes integrals on forums so those so they aren't a terrible pain to read? :)

@hgfalling: Do you think there was a typo in text or did I make a really dumb mistake?

Edit: I've went to wolfram alpha and got the same result. Should I in the future use similar notation to that accepted by wolfram?

http://img717.imageshack.us/img717/7077/integral2.png [Broken]

Last edited by a moderator: May 4, 2017
5. May 23, 2010

### SimpliciusH

6. May 23, 2010

### tiny-tim

Hi SimpliciusH!

have an integral: ∫ and try using the X2 tag just above the Reply box )

You may have fooled Wolfram, but you can't fool us

you can't integrate over a variable and then put the variable back in as a limit of integration …

0kx f(x) dx doesn't make sense.

7. May 23, 2010

### gabbagabbahey

Are you sure the integral isn't $$\int_0^a\int_0^{kx}xy^2dydx$$? As tinytim said, it is very bad notation to have an integral over $x$ and have $x$ in your integration limits.