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# A level C3 - What is this formula used for?I have never had to use it! Watch

1. I saw this formula in the formula book that is provided for the exam, and have never had to use it so far. Can someone explain what its for/ give an example of a question?
2. (Original post by lordoftheties)
I saw this formula in the formula book that is provided for the exam, and have never had to use it so far. Can someone explain what its for/ give an example of a question?
What is it?
3. (Original post by SeanFM)
What is it?
4. (Original post by lordoftheties)
I think it is in the C3 textbook somewhere.

I know integration doesn't really feature in C3, but you might be asked to integrate something like 2sin(7x)cos(x).
5. (Original post by SeanFM)
I think it is in the C3 textbook somewhere.

I know integration doesn't really feature in C3, but you might be asked to integrate something like 2sin(7x)cos(x).
Not absolutely necessary though as you can integrate using parts.
6. (Original post by B_9710)
Not absolutely necessary though as you can integrate using parts.
Hmm.. wouldn't you be trying to integrate either 2sin(7x)sin(x) or (2/7)cos(7x)cos(x) in IBP?
7. It's trig formulaes. The question will Normally give A or B (of either one or both cos/sin) & u use right angled triangles to work out the other.
Then sub into the formulae.

Sorry I can't really explain it well but I hope it helped
8. (Original post by SeanFM)
Hmm.. wouldn't you be trying to integrate either 2sin(7x)sin(x) or (2/7)cos(7x)cos(x) in IBP?
You might be right. I cba to try it though tbh. Leicester not wining has done me in for the day.
9. (Original post by B_9710)
You might be right. I cba to try it though tbh. Leicester not wining has done me in for the day.
I'm not sure Drinkwater deserved to get sent off it's just delaying the inevitable by at least one day anyway

But yes, I think IBP would just send you in circles.

OP, it may come up in one of those 'show that' questions, or if you have something that you can't seem to intergrate then look at these.
10. (Original post by SeanFM)
I'm not sure Drinkwater deserved to get sent off it's just delaying the inevitable by at least one day anyway

But yes, I think IBP would just send you in circles.

OP, it may come up in one of those 'show that' questions, or if you have something that you can't seem to intergrate then look at these.
I personally would prefer to use the formulae above than use parts anyway, even if you can do by parts.
The second booking was a bit harsh but as it was given it should really have been a penalty. I was so relieved it wasn't
11. I have never had to use it and have the feeling that Ive been using an alternative for the questions that ask for it - a correct alternative might I add.

Ill take all the red cards the refs give out against Leicester. COME ON YOU SPURS.
12. (Original post by lordoftheties)
I have never had to use it and have the feeling that Ive been using an alternative for the questions that ask for it - a correct alternative might I add.
It's no on spec anymore. You can use it as an alternative method, but there will never be a question where the intended method is using these formulae.
13. (Original post by B_9710)
I personally would prefer to use the formulae above than use parts anyway, even if you can do by parts.
The second booking was a bit harsh but as it was given it should really have been a penalty. I was so relieved it wasn't
Yes, seems like much less work to use the formula

(Original post by lordoftheties)
I saw this formula in the formula book that is provided for the exam, and have never had to use it so far. Can someone explain what its for/ give an example of a question?
Not the best example, but here is where it has been used in an exam (FP2, Q3). The integral of 3cos2xsinx has been turned into (3/2) sin3x - sinx. Just something you have to know, possibly for C4.
14. (Original post by SeanFM)
Just something you have to know, possibly for C4.
It's not on spec anymore.
15. (Original post by Zacken)
It's not on spec anymore.
Ah, fair enough useful as an alternative method then, as you said

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