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Differentiation of fractions.

Hi guys, im a little bit stuck.

how would you differentiate

2x+3
-------
x

I had 2-3x^-2

Also, would it be ok if you do it step by step so i can see where i went wrong
(edited 12 years ago)
Reply 1
Quotient rule

Diff u/v

=( vu' - v'u )/v^2
Reply 2
Though tbh with the one given I would split the numerator and then you have 2 easy things to differentiate
Reply 3
Original post by TenOfThem
Though tbh with the one given I would split the numerator and then you have 2 easy things to differentiate


Ok. Would it ok if you expand on that, maybe provide a visual? Like how you would it.
Reply 4
Original post by Aillias
Hi guys, im a little bit stuck.

how would you differentiate

2x+3
-------
x

I had 2-3x^-2

Also, would it be ok if you do it step by step so i can see where i went wrong


2x+3x=2+3x\frac{2x + 3}{x} = 2 + \frac{3}{x} which is basically 2+3x12 + 3x^{-1} using laws of indices.

Can you differentiate this function now?
Reply 5
Example

(3x^2-5)/x

=

3x^2/x -5/x

=

3x -5x^-1

Diff this = 3 + 5x^-2

= 3 + 5/x^2
Reply 6
Original post by Aillias
Ok. Would it ok if you expand on that, maybe provide a visual? Like how you would it.


2x+3x=2xx+3x\frac{2x+3}{x}= \frac{2x}{x}+\frac{3}{x}
Reply 7
Original post by Femto
2x+3x=2+3x\frac{2x + 3}{x} = 2 + \frac{3}{x} which is basically 2+3x12 + 3x^{-1} using laws of indices.

Can you differentiate this function now?


I know the answer is -3x^-2, but i just don't understand where the 2 has gone.
This might be really easy to you, but i've just started this topic, today. So, please just bear with me if i don't understand it.
Reply 8
Original post by Aillias
I know the answer is -3x^-2, but i just don't understand where the 2 has gone.
This might be really easy to you, but i've just started this topic, today. So, please just bear with me if i don't understand it.


If you differentiate a constant it disappears
Reply 9
Original post by TenOfThem
If you differentiate a constant it disappears


oh, so the 2 is like c in the formula ax^2+bx+c? and then becomes Dy/Dx = 2ax + b, but the c is missed out since it's a constant, and therefore is 0, well, that's what i have in my book anyway.
Original post by Aillias
oh, so the 2 is like c in the formula ax^2+bx+c? and then becomes Dy/Dx = 2ax + b, but the c is missed out since it's a constant, and therefore is 0, well, that's what i have in my book anyway.


Yes
Reply 11
Original post by Aillias
I know the answer is -3x^-2, but i just don't understand where the 2 has gone.
This might be really easy to you, but i've just started this topic, today. So, please just bear with me if i don't understand it.


You can think of 2 as being the same as 2x^0.
x^0 is always 1, no matter what x is, so that is why those two things above are the same.
If you try differentiating 2x^0, then you get 0, since you have to multiply the whole expression by 0 as part of differentiation. That's why a constant will always disappear when you differentiate it.
Reply 12
Original post by TenOfThem
Yes


Woot, thanks a lot. Rep up!
Reply 13
Original post by Jarred
You can think of 2 as being the same as 2x^0.
x^0 is always 1, no matter what x is, so that is why those two things above are the same.
If you try differentiating 2x^0, then you get 0, since you have to multiply the whole expression by 0 as part of differentiation. That's why a constant will always disappear when you differentiate it.


Thanks for the explanation, I understand it a lot more thanks to you rather than this book. I really need to buy a new maths a level book. What book would you suggest and where could i buy it from? Cos the one i have now is Edexcel Maths A level 2004 specification, and it only has 1 example for questions like this, and it explains it in a really weird way.
Reply 14
Original post by Aillias
Thanks for the explanation, I understand it a lot more thanks to you rather than this book. I really need to buy a new maths a level book. What book would you suggest and where could i buy it from? Cos the one i have now is Edexcel Maths A level 2004 specification, and it only has 1 example for questions like this, and it explains it in a really weird way.


I'm on the AQA course so I'm not sure which book would be best for your course. Maybe ask your teacher if they have any idea on which one would be the best for you. But if your course is anything like mine, then there probably aren't many books available, my course only has 2 per module at a maximum.
Reply 15
Ahh that's ok. Thanks for all your help anyway.

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