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C4 - Differential equation question! Watch

1. Ok i actaully dont get this... the question is question 8a) on the june 07 paper: http://store.aqa.org.uk/qual/gce/pdf...W-QP-JUN07.PDF

ive looked at the mark scheme here: http://store.aqa.org.uk/qual/gce/pdf...W-MS-JUN07.PDF

for the k value i got 2 but i dont understand where it went after that...

after seperating the variables and intergrating i get 2√1+2y = -1/x + c
but on the mark scheme the 2 isn't there, so im a bit confused someone help me out please! thanks
2. (Original post by Gary)
Ok i actaully dont get this... the question is question 8a) on the june 07 paper: http://store.aqa.org.uk/qual/gce/pdf...W-QP-JUN07.PDF

ive looked at the mark scheme here: http://store.aqa.org.uk/qual/gce/pdf...W-MS-JUN07.PDF

for the k value i got 2 but i dont understand where it went after that...

after seperating the variables and intergrating i get 2√1+2y = -1/x + c
but on the mark scheme the 2 isn't there, so im a bit confused someone help me out please! thanks
Because you haven't integrated correctly.

Remember when you integrate a term in brackets you must divide by the differential of what is inside the brackets. In this case that is 2, which will cancel out the 2 which you should not have.
3. (Original post by Gary)
Ok i actaully dont get this... the question is question 8a) on the june 07 paper: http://store.aqa.org.uk/qual/gce/pdf...W-QP-JUN07.PDF

ive looked at the mark scheme here: http://store.aqa.org.uk/qual/gce/pdf...W-MS-JUN07.PDF

for the k value i got 2 but i dont understand where it went after that...

after seperating the variables and intergrating i get 2√1+2y = -1/x + c
but on the mark scheme the 2 isn't there, so im a bit confused someone help me out please! thanks

4. (Original post by Indeterminate)

I don't follow, why are you trying to differentiate that?
5. (Original post by Anythingoo1)
I don't follow, why are you trying to differentiate that?
To show that we get an extra 2

Recall the fundamental theorem of calculus.
6. (Original post by Gary)
Ok i actaully dont get this... the question is question 8a) on the june 07 paper: http://store.aqa.org.uk/qual/gce/pdf...W-QP-JUN07.PDF

ive looked at the mark scheme here: http://store.aqa.org.uk/qual/gce/pdf...W-MS-JUN07.PDF

for the k value i got 2 but i dont understand where it went after that...

after seperating the variables and intergrating i get 2√1+2y = -1/x + c
but on the mark scheme the 2 isn't there, so im a bit confused someone help me out please! thanks
You are on the right way but integrating the LHS do not foget that
there is a composite function over there
that is

but

Generally if
then

which follows from the rules for differentiation.
7. (Original post by Indeterminate)
To show that we get an extra 2

Recall the fundamental theorem of calculus.
Aaaah, working in reverse, I got it (unless what I just said is wrong, in which case I haven't got it )
8. Ohhhh yeahh! Ok I get it now, thank you very much

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9. So basically does that mean whenever I integrate something with like 1 divided by a linear equation , then I integrate and divide the whole thing by the value which is in front on the x? If you get me ....

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10. (Original post by Gary)
So basically does that mean whenever I integrate something with like 1 divided by a linear equation , then I integrate and divide the whole thing by the value which is in front on the x? If you get me ....

Posted from TSR Mobile
Yes

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