Edexcel C3,C4 June 2013 Thread

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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. :smile:

(edited 11 years ago)

Reply 321

Converse girl

Original post by justinawe

use the substitution

u= \sec^2 x

Original post by brittanna

This is in the form

f'(x)f(x)

. Try considering

tan^2(x)

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. :smile:

i got sec^2x :redface:

Reply 322

usycool1

Original post by Converse girl

i got sec^2x :redface:

+C

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

Reply 323

justinawe

Original post by Converse girl

i got sec^2x :redface:

Close, but you forgot a part of it :tongue:

remember

\displaystyle \int x^n \mathrm{ \ } dx = \frac{x^{n+1}}{n+1} + C

Reply 324

QwertyG

Original post by Converse girl

i got sec^2x :redface:

I got tan^2x/2 + c I used u=tanx someone confirm please

Reply 325

usycool1

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. :yy:

Reply 326

Converse girl

Original post by usycool1

+C

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

Original post by justinawe

Close, but you forgot a part of it :tongue:

remember

\displaystyle \int x^n \mathrm{ \ } dx = \frac{x^{n+1}}{n+1} + C

oh yeah i get it always forget +C

thanks guys
i need a lot of practice with intergration :stomp:

Reply 327

QwertyG

Original post by usycool1

That's right too, just with a different constant. :yy:

If you done it with substitution would you have used u=tanx or u=sec^2x?

Reply 328

justinawe

Original post by QwertyG

If you done it with substitution would you have used u=tanx or u=sec^2x?

I would have used

u= \tan x

looking at the question properly. I said

u = \sec^2 x

earlier but wasn't really thinking, the former would have been much easier.

Reply 329

otrivine

Original post by usycool1

+C

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

I see what you mean now! I used integration by parts 3 times and still continues :s-smilie:

Reply 330

Fortitude

Original post by otrivine

I see what you mean now! I used integration by parts 3 times and still continues :s-smilie:

By parts 3 times?!! :eek:

Reply 331

usycool1

Original post by otrivine

I see what you mean now! I used integration by parts 3 times and still continues :s-smilie:

Here's how you can do it (solution in spoiler):

Spoiler

Reply 332

.raiden.

Original post by usycool1

Here's how you can do it (solution in spoiler):

Spoiler

I lost what was going on after line 2 :s-smilie:

Oh wait never mind i get it :smile:

(edited 11 years ago)

Reply 333

AishaTara

how far is evryone through c3 and c4 revision?

Reply 334

otrivine

Original post by usycool1

Here's how you can do it (solution in spoiler):

Spoiler

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? :confused:

Reply 335

posthumus

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? :confused:

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 ?

Reply 336

otrivine

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

Reply 337

.raiden.