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# differentiation c3 helppp watch

1. im getting the wrong answer. Can someone tell me what im doing wrong?
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2. (Original post by JSM1)
im getting the wrong answer. Can someone tell me what im doing wrong?
The error is in your fourth line, when you factorise out (2x + 1)^(-2).

3. I've just started this topic in school too not sure if I'm right did it without a calculator lol
(Original post by JSM1)
im getting the wrong answer. Can someone tell me what im doing wrong?
4. (Original post by Pangol)
The error is in your fourth line, when you factorise out (2x + 1)^(-2).
what have i done wrong? I used the exact method in previous questions where you expand
5. (Original post by JSM1)
what have i done wrong? I used the exact method in previous questions where you expand
You are factorising something that has the form A x^(-2) + B x^(-1). If you factorised x^(-2) out of this, what would you have?

(It's not a huge error, but one missing symbol has lead you to head off in the wrong direction.)
6. (Original post by Pangol)
You are factorising something that has the form A x^(-2) + B x^(-1). If you factorised x^(-2) out of this, what would you have?

(It's not a huge error, but one missing symbol has lead you to head off in the wrong direction.)
7. help
8. (Original post by JSM1)
Sorry - thought I had replied to this. I think you are right, but what do you mean by "the terms"? They change their form after factorising.
9. (Original post by Pangol)
Sorry - thought I had replied to this. I think you are right, but what do you mean by "the terms"? They change their form after factorising.
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10. (Original post by JSM1)
Yeah, that's the bit that is wrong. You should be adding the (-2x + 2) and the (2x + 1), not multiplying them - but even if you were supposed to be multiplying them (which you are not!), there should be a bracket around the first part.
11. (Original post by Pangol)
Yeah, that's the bit that is wrong. You should be adding the (-2x + 2) and the (2x + 1), not multiplying them - but even if you were supposed to be multiplying them (which you are not!), there should be a bracket around the first part.
do you know the reason why you add these terms as in previous questions i expanded the bracket by the number in front of it.
12. (Original post by JSM1)
do you know the reason why you add these terms as in previous questions i expanded the bracket by the number in front of it.
I can't be sure without seeing the question, but I expect you got the right answer by coincidence.

This is just factorisation. In the example I mentioned above, A x^(-2) + B x^(-1), we can factorise out x^(-2) from both terms. How many of these do we have? In the first term, we have A of them. In the second term, we have Bx of them. So altogether, we have A + Bx of them, that is, A x^(-2) + B x^(-1) = x^(-2) [A + Bx].
13. (Original post by Pangol)
I can't be sure without seeing the question, but I expect you got the right answer by coincidence.

This is just factorisation. In the example I mentioned above, A x^(-2) + B x^(-1), we can factorise out x^(-2) from both terms. How many of these do we have? In the first term, we have A of them. In the second term, we have Bx of them. So altogether, we have A + Bx of them, that is, A x^(-2) + B x^(-1) = x^(-2) [A + Bx].
Question:

Find the value of dy/dx at the point x=2 on the curve with the equation

y=(x-1)(2x+1)^-1
14. (Original post by JSM1)
Question:

Find the value of dy/dx at the point x=2 on the curve with the equation

y=(x-1)(2x+1)^-1
Yeah, well to check this I'd need to do the whole thing! I'd rather see your working. But more to the point - do you get what I am saying about factorisation?
15. (Original post by Pangol)
Yeah, well to check this I'd need to do the whole thing! I'd rather see your working. But more to the point - do you get what I am saying about factorisation?
yes i do understand abit but previous questions have the same format so why do you multiply for those
16. this is the other question.
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17. over here i have multiplied out 1(2x+1) which gave me 2x+1,

then adding 1x.. 2x+1+1x gave me........... 3x+1
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18. help?
19. (Original post by JSM1)
over here i have multiplied out 1(2x+1) which gave me 2x+1,

then adding 1x.. 2x+1+1x gave me........... 3x+1
This is right. When you factorise out the 3(2x + 1)^(-1/2), you are left with x from the first term, and 2x + 1 from the second term. You then correctly add these together.

In the problem question, you are left with -2x + 2 from the first term, and 2x + 1 from the second term. You should be adding these together. What you have done is a strange mixture of taking the -2x from the first term, and multiplying the second term by the 2 from the first term.
20. (Original post by JSM1)
help?
Have a bit of patience! There was only four minutes between this and your previous post!

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