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# Edexcel C3,C4 June 2013 Thread watch

1. (Original post by Converse girl)
hi guys can you help me out iam having trouble intergratiting sec^2xtanx
You could do it by substitution or, more quickly, by recognition. There are two possible answers for this, btw, there's just a different constant for both answers.
2. (Original post by justinawe)
use the substitution

(Original post by brittanna)
This is in the form . Try considering .

(Original post by usycool1)
You could do it by substitution or, more quickly, by recognition. There are two possible answers for this, btw, there's just a different constant for both answers.
i got sec^2x
3. (Original post by Converse girl)
i got sec^2x
+C

And you should have got (1/2)sec^2 x + C...what did you do to get that answer?
4. (Original post by Converse girl)
i got sec^2x
Close, but you forgot a part of it

remember
5. (Original post by Converse girl)
i got sec^2x
I got tan^2x/2 + c I used u=tanx someone confirm please
6. (Original post by QwertyG)
I got tan^2x/2 + c I used u=tanx someone confirm please
That's right too, just with a different constant.
7. (Original post by usycool1)
+C

And you should have got (1/2)sec^2 x + C...what did you do to get that answer?

(Original post by justinawe)
Close, but you forgot a part of it

remember
oh yeah i get it always forget +C

thanks guys
i need a lot of practice with intergration
8. (Original post by usycool1)
That's right too, just with a different constant.
If you done it with substitution would you have used u=tanx or u=sec^2x?
9. (Original post by QwertyG)
If you done it with substitution would you have used u=tanx or u=sec^2x?
I would have used looking at the question properly. I said earlier but wasn't really thinking, the former would have been much easier.
10. (Original post by usycool1)
+C

And you should have got (1/2)sec^2 x + C...what did you do to get that answer?
I see what you mean now! I used integration by parts 3 times and still continues
11. (Original post by otrivine)
I see what you mean now! I used integration by parts 3 times and still continues
By parts 3 times?!!
12. (Original post by otrivine)
I see what you mean now! I used integration by parts 3 times and still continues
Here's how you can do it (solution in spoiler):

Spoiler:
Show

Use integration by parts. Let "u" equal and

So...

and v =

So you should get (after using integration by parts):

Which is the same as:

Now use integration by parts again to get:

Expand the brackets to get:

OK, now we'll go on forever and ever if we keep using integration by parts. So:

To make things a tiny bit easier, let I =

So we have:

Take the "I" terms onto one side:

Now "solve" for I:

So after "dividing" both sides by , you should eventually (after simplifying a bit) get:

13. (Original post by usycool1)
Here's how you can do it (solution in spoiler):

Spoiler:
Show

Use integration by parts. Let "u" equal and

So...

and v =

So you should get (after using integration by parts):

Which is the same as:

Now use integration by parts again to get:

Expand the brackets to get:

OK, now we'll go on forever and ever if we keep using integration by parts. So:

To make things a tiny bit easier, let I =

So we have:

Take the "I" terms onto one side:

Now "solve" for I:

So after "dividing" both sides by , you should eventually (after simplifying a bit) get:

I lost what was going on after line 2

Oh wait never mind i get it
14. how far is evryone through c3 and c4 revision?
15. (Original post by usycool1)
Here's how you can do it (solution in spoiler):

Spoiler:
Show

Use integration by parts. Let "u" equal and

So...

and v =

So you should get (after using integration by parts):

Which is the same as:

Now use integration by parts again to get:

Expand the brackets to get:

OK, now we'll go on forever and ever if we keep using integration by parts. So:

To make things a tiny bit easier, let I =

So we have:

Take the "I" terms onto one side:

Now "solve" for I:

So after "dividing" both sides by , you should eventually (after simplifying a bit) get:

wow! wait, can i now just use substitution, my integration by parts was the same as urs but do not get then how you or why you considered I?
16. (Original post by otrivine)
wow! wait, can i now just use substitution, my integration by parts was the same as urs but do not get then how you or why you considered I?
Its quite unlikely to come up if you ask me - I don't think it has ever before... where did you get the question from ?
17. (Original post by posthumus)
Its quite unlikely to come up if you ask me - I don't think it has ever before... where did you get the question from ?
Usycool1 asked this question and I was trying to solve it!

By the way on page on differenitation example 4! I think they made a mistake ,can you or anyone confirm this.

The question was

find the valie of dy/dx at point (1,1)

where 4xy2 +6x2/y = 10
18. (Original post by otrivine)
Usycool1 asked this question and I was trying to solve it!

By the way on page on differenitation example 4! I think they made a mistake ,can you or anyone confirm this.

The question was

find the valie of dy/dx at point (1,1)

where 4xy2 +6x2/y = 10
I checked it, looks right to me
19. (Original post by otrivine)
Usycool1 asked this question and I was trying to solve it!

By the way on page on differenitation example 4! I think they made a mistake ,can you or anyone confirm this.

The question was

find the valie of dy/dx at point (1,1)

where 4xy2 +6x2/y = 10
What answer did you get ?
20. (Original post by raiden95)
I checked it, looks right to me
they got 12x/y but should there not be a y with 12x?

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