Quick maths quee :)

hellarda · 26 Sep 2011 at 20:53

Hi guys,

doing differentiation and got stuck on one question

differentiate:

y=x^2+3x/√x

any ideas?

cheers

ripped · 26 Sep 2011 at 20:54

So, what you got to do? get x?

Mason- · 26 Sep 2011 at 20:57

2x + (3root(x) - 3x/root(x))/x

CBA to check but for quotient rule. if you have u/v

then you do. vdu - udv / v squared.

Emphacy · 26 Sep 2011 at 21:00

OMG I could do this so easily a few months ago

It's amazing how quickly you forget this stuff but you can do that without the quotient rule.

I tried to have a go but I'm stupidly rusty... root(x) can be rewritten as x^(1/2).

Jesus Christ, I've forgotten everything.

gambitt · 26 Sep 2011 at 21:00

It's been a very long time for me but I take it you can't just cancel 3x/√x to 3(√x)?

SlyReaper · 26 Sep 2011 at 21:02

Yes you can. It simplifies to y = x^2+3√x

Thus, dy/dx = 2x + 3/(2√x)

Come on guys, this is rudimentary maths.

Dr Delphi · 26 Sep 2011 at 21:03

http://www.wolframalpha.com/input/?i=differentiate y = x^2 + 3x/SQRT(x)

If you know how to use wolfram alpha then you can differentiate anything - however I would recommend that if it is homework then you should attempt it first before plugging it in. Also check out that this shows you the steps to the correct result as well.

Elixir · 26 Sep 2011 at 21:07

You can do it from there... just remember root(x) = x^1/2, and your rules of powers, x^n / x^m = x^(n-m)

EDIT: Or the way shown above which is the same thing, I prefer to get everything into numbers though.

Emphacy · 26 Sep 2011 at 21:07

SlyReaper said:
Come on guys, this is rudimentary maths.

I could do this, and a whole lot more back in July. Doing a degree and I've forgot everything I did because I did none over summer.

Ironically, I managed to get over 65% in the exam, despite maths being my 'weakest' subject.

Just brushing up on some now TBH.

SlyReaper · 26 Sep 2011 at 21:14

I'm possibly being a bit unfair because I have a maths degree, but this level of maths really does look like child's play to me.

Mason- · 26 Sep 2011 at 21:25

SlyReaper said:
Yes you can. It simplifies to y = x^2+3√x

Thus, dy/dx = 2x + 3/(2√x)

Come on guys, this is rudimentary maths.

Fine, but what I did wasn't wrong.

SlyReaper · 26 Sep 2011 at 21:43

Mason- said:
Fine, but what I did wasn't wrong.

Overcomplicating it, even if you get the right answer == wrong, in my book.

It is perhaps somewhat fortunate that I am not a maths teacher.

TheCenturion · 26 Sep 2011 at 21:54

If you know the product rule, but don't know the quotient rule, you can always just turn it into

(x^2+3x)x^-1/2

and then do it like that.