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# Constant of integration watch

1. Would it be ok:

xsin2x - (intergral) sin2x
xsinx - [-1/2cos2x] + D]
xsin2x + 1/2 cos2x + C

to use +C instead of -D
2. (Original post by 111davey1)
Would it be ok:

xsin2x - (intergral) sin2x
xsinx - [-1/2cos2x] + D]
xsin2x + 1/2 cos2x + C

to use +C instead of -D
Yes you don't have to use a different letter in the exam. But do you understand why they've used a different letter here?
3. It must be a capital C
4. (Original post by notnek)
Yes you don't have to use a different letter in the exam. But do you understand why they've used a different letter here?
Thanks.
Thought so. because C=-D, the + just makes it easier.
5. Yes you are meant to put + C or + c for any general solution.
6. (Original post by Anfanny)
Yes you are meant to put + C or + c for any general solution.
Oh ok but would i be penalised if i put +D?
7. (Original post by 111davey1)
Oh ok but would i be penalised if i put +D?
I think so because + C means aD where a = -1 here so + C makes it look neat as it fits in with what the book is told.
8. (Original post by Anfanny)
I think so because + C means aD where a = -1 here so + C makes it look neat as it fits in with what the book is told.
So the second line i used D. Is that right?
The third line i changed it to +C. Is that right?

Is the problem The letter used or the fact that a - would be introduced if you used -D instead of C
9. C means it's the constant times another constant so just make it plus C no matter what it was before.
10. (Original post by Anfanny)
C means it's the constant times another constant so just make it plus C no matter what it was before.
I used the letter D in the first intergral. Should i have used C and then in the following line C'. And if i needed another C'' or is D fine for the first one.
11. As long as the terms equate is you can write (-D + J - L )etc. and replace the whole thing with + C so yes as long as it is just a number write + C
12. (Original post by Anfanny)
As long as the terms equate is you can write (-D + J - L )etc. and replace the whole thing with + C so yes as long as it is just a number write + C
I still think it would be ok to use +(any letter) in the second line
and then + any letter in the third line because it just represents a different constant
13. Yes okay.
14. (Original post by Anfanny)
Yes okay.
But you have made me unsure...
15. (Original post by 111davey1)
But you have made me unsure...
You're thinking too much about this. Use any letters you want and if you decide to change the letter at some point then that's fine and if you keep it the same then that's also fine.
16. (Original post by Anfanny)
Yes you are meant to put + C or + c for any general solution.
(Original post by Anfanny)
It must be a capital C
(Original post by Anfanny)
I think so because + C means aD where a = -1 here so + C makes it look neat as it fits in with what the book is told.
(Original post by Anfanny)
C means it's the constant times another constant so just make it plus C no matter what it was before.
What the heck?? No, OP wouldn't be penalised if he put +D. He/she can have any letter they want as long as they define it to be the constant of integration. A constant is a constant - the way you represent it doesn't strictly matter unless the questions asks for a specific form, it's just for convenience sake and simplicity that the notion of +c arises. Nothing serious and no mark loss would occur if +c wasn't used as long as there is a constant of integration - please don't confuse OP.
17. I guarantee the examiner will think differently depending on the exam board there are generally accepted rules but okay if a constant is a constant then do whatever that's just what's in my book.
18. (Original post by Anfanny)
I guarantee the examiner will think differently depending on the exam board there are generally accepted rules but okay if a constant is a constant then do whatever that's just what's in my book.
no maths examiner in their right mind will ever deduct a mark for using +D instead of +C (as long as its defined ofc)
19. (Original post by Anfanny)
I guarantee the examiner will think differently depending on the exam board there are generally accepted rules but okay if a constant is a constant then do whatever that's just what's in my book.
This isn't correct. Making confident statements beginning with "I guarantee ..." when you aren't at all sure of your facts is not helpful to the users of this Forum.
20. That's what's in my book and also I don't need to explain with a legend or key what the constant is! Using +C is in the book so that's what I will use.

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