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# Separable differentiation watch

1. Attachment 695170695172

(3i) , so as usual, where did I mess up?
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2. (Original post by ckfeister)

Attachment 695170695172

(3i) , so as usual, where did I mess up?
You had , not (as you treated it)

Instead, divide both sides by , to obtain,

. Should be relatively clear where this is going.
3. (Original post by ckfeister)

(3i) , so as usual, where did I mess up?
To be honest, I'm struggling to make any sense of that at all. What does the (x dx) (-y^2) bit mean?

The first step is to separate the variables i.e. formally write:

then integrate.
4. (Original post by _gcx)
You had , not (as you treated it)

Instead, divide both sides by , to obtain,

. Should be relatively clear where this is going.
I don't get where this is meant to go, whats the link with tanx?
5. (Original post by ckfeister)
I don't get where this is meant to go, whats the link with tanx?
Are you familiar with how to approach

?
6. (Original post by _gcx)
Are you familiar with how to approach

?
Nope... first time. I would try sub but I'm sure it won't get tan(x)
7. (Original post by ckfeister)
Nope... first time.
Have you covered integration by substitution? Try substituting .
8. (Original post by ckfeister)
I don't get where this is meant to go, whats the link with tanx?
Which module are you doing currently?
9. (Original post by notnek)
which module are you doing currently?
aqa - fp2
10. (Original post by ckfeister)
aqa - fp2
Then you'll need to know how to integrate that using a trig substitution and you should also be aware that is in your fomula book.

Do you have any ideas which substitution you can use?
11. (Original post by Notnek)
Then you'll need to know how to integrate that using a trig substitution and you should also be aware that is in your fomula book.

Do you have any ideas which substitution you can use?
x/a tan-1 x/a?
12. (Original post by ckfeister)
u = 1+y^2

du/dy= 2y

du/2y = dy

Only one I know, I'm going to watch a video soon on khan academy but this hasn't been on the lessons yet... strange.
It seems like you haven't covered trig substitutions so you shouldn't be doing this question yet. _gcx has given you the correct substitution above.
13. (Original post by ckfeister)
u = 1+y^2

du/dy= 2y

du/2y = dy

Only one I know, I'm going to watch a video soon on khan academy but this hasn't been on the lessons yet... strange.
Have you covered integration by substitution? Try substituting .
It's not an obvious substitution, but it works quite well as you'll see. Watching a khanacademy video on trig subs, or similar, might be beneficial as you suggested.
14. (Original post by Notnek)
It seems like you haven't covered trig substitutions so you shouldn't be doing this question yet. _gcx has given you the correct substitution above.
(Original post by _gcx)
It's not an obvious substitution, but it works quite well as you'll see. Watching a khanacademy video on trig subs, or similar, might be beneficial as you suggested.
Is it x/a tan-1 x/a?
15. (Original post by ckfeister)
Is it x/a tan-1 x/a?
Not quite, you might have made a slip. Can you show your working? (Also, where has a come from? I'd dissuade you from copying from a formula booklet, it's more beneficial to do it yourself first)
16. (Original post by _gcx)
Not quite, you might have made a slip. Can you show your working? (Also, where has a come from? I'd dissuade you from copying from a formula booklet, it's more beneficial to do it yourself first)
C3 - which I learnt there, I'm going to watch khan academy (£350 course cost doesn't cover this)

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